运动鞋中底用什么改性PP？答案不是"回弹越高越好"。中底要的是在既定步态与体重区间里，让回弹、缓震、耐久三者落进设计窗口。这篇把性能三角、POE 复配在调什么、八项判据与逐级验证顺序摆清楚，并说明哪三种情况这个件不该用发泡 PP。
- 对照说明：贸易版 87 篇无鞋材板块，本篇无同主题对照篇；差异点在系列内部错开
"鞋中底用什么改性PP，是不是看回弹率就行？"
一个做鞋底配套的技术员这么问我，随后把曲线发了过来。曲线不难看，落球回弹落在偏高的一档。他没说的是，这个件是稳定支撑型，目标人群是大体重慢跑。
鞋中底最容易走偏的地方就在这里：它要的是"按设计曲线回弹"，不是"回弹越高越好"。
同一块中底上，"回弹高"和"缓震好"天生是一对反向指标，想要一头，另一头就得让。回弹堆得太高，卸载时能量快速还给脚，瞬时反馈变尖，穿感就是"顶脚"，稳定性跟着变差。
别的发泡件不是这个逻辑。缓冲垫要的是峰值力低，包装件要的是吸能；鞋中底要的是在某一种步态、某一段体重区间里，回弹与缓震的组合落进设计窗口。
下面按工况、三角、配方、判据、验证五层往下拆。
一、运动鞋中底的工况六维：温度有两头，载荷是反复的
先说结论：鞋中底最特殊的一维是寿命——它不按年份算，按里程和步数算。
| 维度 | 鞋中底的实际工况 | 对材料的要求 |
|---|
| 温度 | 下限常见 −20℃（北方冬季户外）；上限夏季地面与鞋内可到 40-50℃；成品鞋还有仓储存放温度 | 低温不脆裂、低温回弹衰减可控；高温不塌陷 |
| 载荷 | 体重（常见 50-90 kg 级）+ 落地冲击（跑步峰值可达体重的 2-3 倍级）+ 每公里千次级的反复压缩 | 压缩永久变形小、动态疲劳后刚度衰减慢 |
| 介质 | 汗液（偏酸、含盐）、雨水、清洁剂；洗鞋时的浸泡与刷洗 | 耐水解、耐盐、耐清洁剂，不析出不发粘 |
| 寿命 | 按里程算：训练鞋常见按 500-800 km 级的衰减窗口设计；休闲鞋按年 | 衰减曲线要平，不能前 100 km 好、后面塌 |
| 外观 | 白色中底是主流；长期存放与光照后发黄是常见客诉；批次间色差 | 耐黄变、色差可控 |
| 合规 | 鞋材与皮肤接触的相关要求；成品鞋在密闭鞋盒里的气味与 VOC | 配方要过接触与气味两道口径 |
六个维度里最反常识的是寿命。别的件按"用了几年"算，鞋中底按"跑了多少公里"算。客户投诉的原话往往不是"寿命不够"，是"跑三百公里就踩不动了"——这句话里藏着两个指标，第六节拆开讲。
一个内行细节：中底的前掌与后跟衰减速度不一样。后跟载荷高，压缩永久变形累积更快；前掌弯折次数多，是耐折薄弱区。中底很少整块均匀坏掉，而是某一个分区先失效——按整块取样验收，最容易把最差那区测没了。
二、鞋中底的性能三角：回弹、缓震、耐久不可能同时拉满
先说结论：回弹、缓震、耐久是三条互相拉扯的线，同一块中底不可能三条都拉满。
回弹是能量回馈率。跑鞋追求高回弹，因为要"还"能量。但回弹太高有两个代价：卸载时瞬时加速度峰值高，穿感"顶脚"；同密度下泡孔壁更硬，抗压缩疲劳的余地变小。
缓震是冲击吸收，本质是滞后损失：加载与卸载的面积差越大，耗掉的能量越多。缓震好就意味着回弹低，这是一枚硬币的两面。
耐久是压缩永久变形，反复压缩后能不能回到原位。这一项才是真实投诉最主要的来源。
三条线的对拉关系，可以写成一张兑换表。
| 动作 | 回弹 | 缓震 | 耐久 | 其他代价 |
|---|
| 提高发泡倍率（降密度） | 略升 | ↓ | ↓ | 压缩强度与厚度保持同时掉 |
| 提高弹性体（POE）配比 | 先升后平 | ↑ | ↑（适度范围内） | 熔体强度与耐热下降、成本上升 |
| 提高基材结晶度 / 硬度 | ↑ | ↓ | ↑ | 低温更硬、缓震更差 |
| 提高硬段比例 / 交联程度 | ↑ | ↓ | ↑↑ | 工艺窗口变窄、回收性变差 |
文字版结论：最该记住的是第一行和最后一行。降密度是鞋材第一诉求，但它同时扣缓震和耐久；提交联能同时提回弹和耐久，代价落在工艺与回收上。改性PP 中底选型，第一步就是定这三条线的位置关系。
敢否定一个常见做法： 拿"回弹率越高越好"当选型判据，是市场话术，不是工程判据。工程上要的是在这个鞋型的步态与体重区间内，回弹与缓震的组合落进设计窗口——竞速鞋要高回弹低滞后，稳定支撑鞋要缓震优先，用同一张回弹榜去排，必然排错。
还有一条更少人提：低温下弹性体的回弹会下降。温度低，分子链段活动性降下来，模量上升，落地冲击峰值反而更尖（据行业媒体公开资料，B 级）。按常温定的窗口，到 −20℃ 可能整段偏出去——北方冬季的体感差异是真实存在的。
三、发泡 PP 与 POE 复配：POE 在调什么，代价在哪
先说结论：纯 PP 发泡有两个结构性短板，POE 复配各补一半；但 POE 加多了，会反过来伤熔体强度和耐热。
PP 是结晶性聚合物，熔体强度低。发泡时泡孔壁被拉伸减薄，容易被拉破，结果是泡孔不均匀、局部塌陷、并孔。纯 PP 又偏硬，回弹快但缓震差，直接做中底脚感像一块板。
POE 补的第一件事是熔体强度与弹性，让泡孔在生长阶段撑得住。公开期刊的 PP／弹性体发泡研究里有这条规律：纯 PP 发泡的泡孔密度约 2.62×10⁶ 个/cm³、平均孔径约 55.36 μm；加到 20 wt% 弹性体后，泡孔密度升到约 12.5×10⁶ 个/cm³、孔径降到约 25.42 μm（据公开期刊数据，A 级）。同样叫发泡 PP，泡孔结构能差一个量级——"两家都报发泡 PP，脚感完全不同"就是这么来的。
POE 补的第二件事是降刚度、提缓震。改性PP 做发泡基材，POE 复配是当前的主流做法。
代价有三条。一是相容性：POE 主链偏聚乙烯型，与 PP 相容性有限，需要增容（公开期刊常用 PP-g-MAH，A 级）。二是加多了连续相骨架会变弱：公开专利写明，含量低时回弹改善不明显；含量高时骨架变弱、耐热下降、发泡时容易收缩塌陷，优选质量比 PP : α-烯烃弹性体 =（50-75）:（25-50）（A 级）。三是成本——POE 单价高于 PP。
文字版结论：POE 是"调时间常数和刚度"的工具，加量由压缩永久变形 + 回弹速度 + 刚性下限三条一起定。天花板不是配方师拍的，是这个鞋型能接受的最低刚度定的。
发泡工艺这一层也要先分清。 物理发泡（超临界 CO₂／N₂）以气体作发泡剂，超临界 CO₂ 的临界参数约为 31.1℃／7.38 MPa（公开物理常数），泡孔更细密均匀、无化学残留。化学发泡（AC 类）工艺简单、成本低，代价是分解残留与气味。高端中底主流动向是物理发泡，普通中底仍大量用化学发泡——这是分工，不是优劣。至于具体工艺参数（饱和温度、压力、含气量、泄压速率），必须按设备与配方实测确认。
四、材料路线对比：发泡 PP 与 EVA、PU、PEBA、TPEE 的分工边界
先说结论：这些路线解决的不是同一类问题——按"要解决什么"分，不按"谁更好"分。
| 路线 / 材料 | 拿到什么 | 代价 / 边界 |
|---|
| 发泡 PP（珠粒类，EPP 体系） | 密度低、回弹中上、抗压缩疲劳好、尺寸稳定；PP 是热塑性体系，废料理论上可再熔融加工 | 熔体强度低需配方补；刚度偏高、缓震一般；发泡窗口窄 |
| PP + POE 复配发泡（本篇主线） | 泡孔更细匀、刚度降下来、缓震改善、低温韧性更好 | 需增容；加多伤熔体强度与耐热；成本上升 |
| EVA（含 POE-EVA 共混） | 工艺最成熟、成本低、柔软，休闲鞋主流 | 回弹与耐久是短板，长期穿着易"踩扁"（据行业媒体公开资料，B 级） |
| PU / 超临界 PU | 回弹与耐久均衡，压缩永久变形表现好 | 同等倍率下密度偏高、脚感偏实；交联体系的残留与回收是另一笔账 |
| PEBA（尼龙弹性体） | 同倍率下密度更低、能量回馈更高、温域更宽 | 成本高，常见做法是与 EVA／TPU 共混降本 |
| TPEE / TPU 珠粒 | 耐久与回弹均衡，珠粒与板材路线都成熟 | 密度与脚感偏实；上游工艺集中度高 |
| 橡胶底材（硫化体系） | 耐磨、抓地、耐折 | 密度高、回弹低，多用于大底而非中底 |
文字版结论：EVA 与 PU 是国内鞋材的主流，改性PP 基体系是后进入者，靠的是"更轻 + 热塑性可回收 + 抗压缩疲劳"。选路线先回答：这个件最不能掉的是哪一条？回弹优先看 PEBA／超临界体系，成本与柔软优先看 EVA，轻量与回收优先看改性PP 基，均衡耐久看 PU／TPU。
五、★ 选型判据表：运动鞋中底七项指标，每项都带验证方法
先说结论：这张表最该先看第三列——鞋中底的难点不是"看哪个指标"，是"拿哪套鞋类方法测"。
| 指标 | 门限值（典型） | 验证方法 · 标准号 | 常见失效 | 通行解法 |
|---|
| 表观密度 | 按鞋型定窗口；公开行业媒体口径：EVA 基 0.08-0.12 g/cm³、PEBA 基 0.07-0.10、TPU 基 0.05-0.13（B 级，口径不同不可直接对比） | GB/T 6343 | 密度上浮→超重；下探→压缩强度与耐久同掉 | 按"密度-性能"曲线定窗口，不追单一低密度值 |
| 落球回弹率 | 按鞋型定窗口；公开资料中 PEBA 板材实测约 73-76%（B 级，需回原文复核） | GB/T 6670-2008（φ16 mm／16 g 钢球、500 mm 落高，试样调节 ≥24 h，测 3 次取均值） | 偏高→顶脚、稳定性差；偏低→泄力 | 用 POE 配比与泡孔结构把回弹收进窗口 |
| 压缩永久变形 | 按循环与温度口径定；公开资料中一类板材按（50%／6 h／50℃）报 18-23%（B 级） | GB/T 6669-2008（压缩至 50% 或 75%、70℃×22 h、恢复 30 min 测残余变形） | 跑几百公里后"踩不动"、厚度与预压力损失 | 弹性体配比 + 泡孔细化 + 基材档位一起调 |
| 尺寸与批次一致 | 按贴合线与装配公差定；密度与尺寸是联动量，批次密度波动要有上限 | 密度按 GB/T 6343 逐批比对；尺寸按图纸全检口径 | 贴合良率波动、厚度超差 | 控密度窗口 + 批次数据卡 |
| 耐折 | 按整鞋或鞋底耐折方法验证；标准不含跟高 >70 mm 或屈挠部位厚度 >25 mm 的件 | GB/T 3903.1-2017《鞋类 整鞋试验方法 耐折性能》 | 前掌屈挠处开裂、泡孔壁断裂 | 提高弹性体配比 + 优化前掌密度 |
| 低温性能 | 按最低使用温度定；低温下回弹下降、模量上升，冲击峰值变尖（B 级） | 低温预处理后按 GB/T 3903.1-2017 弯折 + 低温回弹对比 | 冬季变硬、开裂 | 选低温更好的基材或弹性体体系 |
| 耐黄变与气味 | 黄变等级常见验收 ≥3-4 级（B 级，以客户验收文件为准）；气味按客户口径，可引 VDA 270 气味 ≤3 级作旁证（非国标） | 黄变按 HG/T 3689-2014（方法 A 太阳灯法／方法 B 紫外灯管法；箱温 50±2℃、湿度 65±5%，光照后 30 min 内比色）；气味按 VDA 270 | 白色中底长期存放或光照后发黄；开箱气味重 | 抗氧体系、避开易黄变助剂；少用化学发泡剂，控脱模剂与低分子助剂 |
文字版结论：七项里压缩永久变形与耐黄变最容易被排到最后——前者贴近真实投诉，后者与"性能"无关却最要命。这张表当体检单用，缺一项不判合格。
六、常见失效与根因：鞋中底四个现象，四条根因
先说结论：四类失效里只有一类是"料不对"，另外三类分别出在目标窗口、助剂体系和取样方式上。
失效一：跑了三百公里"踩不动了"。 客户说"变硬了"，本质是泡孔结构塌陷 + 压缩永久变形——厚度回不去，预压力损失。判据在压缩永久变形（GB/T 6669 口径），不在回弹率。拿回弹率解释这个现象，方向从一开始就错了。
失效二：刚上脚就说"顶脚"。 这不是回弹不够，恰恰是回弹偏高、滞后损失偏小——先看这个鞋型的设计窗口，别急着换更软的料。
失效三：白色中底发黄。 与性能无关，商业上却很要命。先看助剂体系（抗氧剂与易黄变组分），再看发泡路线——化学发泡的残留是黄变加速项。判定按 HG/T 3689-2014，光照后 30 分钟内比色，超时判定不作数。
失效四（敢否定一个常见做法）：用整块中底取样去验收性能。 中底很少均匀失效——后跟压缩变形累积快，前掌耐折负担重。整块取样取的是平均值，而投诉永远出在最差的那一个分区。 正确做法是按前掌／中腰／后跟分区取样、分区定门限。
七、验证顺序：鞋中底先验什么，后验什么
先说结论：鞋中底最贵的一次失败发生在整鞋阶段，而它的根源偏偏在前两步没做。
| 顺序 | 验证项 | 不过就退回的判据 |
|---|
| ① 定鞋型与目标窗口 | 步态类型、体重区间、目标密度与回弹／缓震窗口 | 窗口没定，后面所有门限都是猜的 → 退回重问 |
| ② 密度与压缩-回弹曲线 | 密度（GB/T 6343）+ 落球回弹（GB/T 6670）+ 压缩应力-应变曲线 | 曲线落不进窗口 → 退回弹性体配比与密度档 |
| ③ 压缩永久变形 | GB/T 6669 口径（50% 或 75%、70℃×22 h、恢复 30 min），按分区取样 | 残余变形超门限 → 退回泡孔结构与配比 |
| ④ 耐折与低温 | GB/T 3903.1-2017 弯折 + 低温预处理后再弯折 + 低温回弹对比 | 屈挠处开裂或低温回弹衰减超限 → 退回基材与弹性体 |
| ⑤ 耐黄变与气味 | HG/T 3689-2014（方法 A／B）；气味按 VDA 270 口径旁证 | 黄变不达门限、气味超标 → 退回助剂与发泡路线 |
| ⑥ 整鞋试穿与耐久 | 按里程／次数做穿着与动态疲劳，看衰减曲线平不平 | 衰减曲线陡 → 回到 ① 重定窗口 |
文字版结论：顺序是 定窗口 → 曲线 → 压缩永久变形 → 耐折与低温 → 耐黄变与气味 → 整鞋试穿。压缩永久变形必须在整鞋之前过，它最可能一票否决，也最贴近投诉原话。
八、反向诚实：这三种情况，鞋中底不该用发泡改性PP
先说结论：只要出现"发泡件拿不到的东西"，就不该硬撑。
第一，要求极高的回弹能量回馈。 竞速鞋中底的能量回馈目标普遍标到 80% 以上，更高端的体系报到 85% 以上（品牌口径，测试标准各异，不可横向对比）。改性PP 基发泡体系的天花板不在同一个位置。 该走 PEBA／超临界 PU／TPEE 这些高回弹体系，或用双密度设计把高回弹层交给别的材料。
第二，要求长期高强度使用下几乎不衰减。 专业竞技的使用强度会把压缩永久变形推到极限。发泡多孔材料的衰减是物理性的，改性只能把曲线拉平，消不掉。 该走 PU／TPU 这类回弹更稳定的体系，或由结构（推进板类）分担衰减。
第三，要求极高的密度精度。 自动化贴合线对密度与厚度波动很敏感。发泡件的密度与尺寸是联动量——密度动，尺寸跟着动，批次密度波动会直接影响这条线的良率。 该先确认发泡路线的批次波动范围，或改用密度更稳的非发泡体系。
九、换料风险清单：发泡 PP 中底换料先看什么
决定试发泡 PP 之前先过一遍这张表。客户真正的顾虑往往不是性能，是"我现在的模具和工艺要不要改"。
| 要动的项 | 需要确认什么 | 不做会怎样 |
|---|
| 成型路线 | 珠粒釜压／板材模压／胚模发大／连续挤出，四条路线的设备与节拍完全不同 | 选了接不住的路线，样件根本做不出来 |
| 收缩与密度 | 密度与尺寸联动，不是固定值；模具基准按哪个密度标定 | 贴合尺寸与厚度对不上 |
| 料温与模温／蒸汽条件 | 泡孔结构与熔结质量对温度、时间、压力都敏感 | 泡孔粗化、熔结不良、局部塌陷 |
| 脱模与脱模剂 | 用量受控，能不用就不用；残留会同时伤气味与洁净 | 气味与析出超标 |
| 色差 | 白色中底必须先确认色板，再做耐黄变验证 | 批次色差争议 |
| 验证顺序 | 定窗口 → 曲线 → 压缩永久变形 → 耐折与低温 → 耐黄变与气味 → 整鞋试穿 | 风险全部集中到整鞋阶段爆发 |
文字版结论：换料要动的是成型路线、工艺窗口、色差三块，其中最该先谈的是验证顺序。跳过曲线直接上整鞋，等于把最贵的那次失败留到最后。
十、一页纸汇报对照表：鞋中底选型可以直接贴进 PPT
先说结论：判断标准只有一条——客户拿这张表，能不能在一次会议里把材料方向定下来。
| 场景 | 推荐路线 | 关键指标 | 验证标准 | 需先确认的条件 |
|---|
| 日常训练鞋中底 | PP + POE 复配发泡，密度按鞋型定 | 落球回弹落进窗口、压缩永久变形留余量 | GB/T 6670、GB/T 6669 | 目标体重区间、步态类型 |
| 稳定支撑型 / 缓震优先 | 回弹往窗口下沿收，缓震优先 | 压缩-回弹曲线偏缓震；分区硬度 | GB/T 6670 + 压缩应力-应变曲线 | 支撑结构设计、分区硬度定义 |
| 北方冬季款 | 低温表现更好的基材或弹性体体系 | 低温回弹衰减 + 低温弯折不裂 | GB/T 3903.1-2017 + 低温回弹对比 | 当地最低气温记录 |
| 白色外观款 | 物理发泡路线 + 抗黄变体系 | 黄变等级达客户门限 | HG/T 3689-2014（方法 A／B） | 客户黄变门限、存放周期 |
文字版结论：这张表的作用是让技术员把结论直接往上报。别把回弹、缓震、耐久三条线都塞进"性能要好"一句里——三条各自给窗口。
十一、这个件上最容易出问题的，往往不是回弹
鞋中底上最常见的两类失效是"踩不动"与"顶脚"，归因都不是"回弹不够"。"踩不动"对应压缩永久变形（GB/T 6669 口径）；"顶脚"对应回弹偏高、滞后损失偏小（GB/T 6670 的落球回弹与压缩-回弹曲线窗口）。
很多"料不行"的结论，最后定位到的是窗口定错，或取样取了整块平均值、把最差那一区测没了。行业通行的做法是把基材档位、弹性体（POE）配比、发泡路线一起定——单看任何一项都没意义，关键是基材档位、弹性体配比、发泡路线、密度窗口四件事能不能同时对上。
宁波市科隆新材料有限公司在这个件上常供的是改性聚丙烯（PP）粒子里的发泡基材方向：按目标窗口给基材档位与 POE 复配比例，按鞋型与工艺路线给低气味、耐黄变的助剂方向建议，主要解决"曲线调不进窗口"与"跑一段就衰减"这两件事；配方按工况调，可配合小样比对与试模。
常见问答
问：回弹率是不是越高越好？
答：不是。回弹高意味着卸载时能量快速返还、反馈更尖，穿感会"顶脚"，稳定性也差。要的是落进这个鞋型的窗口。
问：POE 加多一点，缓震和回弹不都上去了？
答：加过量有两笔代价：POE 与 PP 相容性有限、需增容，加多了骨架变弱、耐热下降，发泡时反而容易塌陷；另外是成本。上限由这个鞋型能接受的最低刚度定。
问：物理发泡一定比化学发泡好？
答：不是。物理发泡无化学残留、泡孔更细匀，代价是设备与控程要求高；化学发泡简单省钱，代价是残留与气味。按产品定位分工。
| 工况 | 关键判据 | 常规供应 |
|---|
| 日常训练鞋中底 | 落球回弹（GB/T 6670）落窗口、压缩永久变形（GB/T 6669）留余量 | 改性PP 发泡基材 + POE 复配方向 |
| 稳定支撑 / 缓震优先 | 压缩-回弹曲线偏缓震、分区硬度 | 发泡基材 + 弹性体配比调整 |
| 白色外观款 | 黄变等级（HG/T 3689-2014） | 低气味、耐黄变助剂方向 |
最后说三句。 头一句，鞋中底要的是"按设计曲线回弹"，不是"回弹越高越好"——三条线只能同时拉满两条。
第二句，"踩不动"是压缩永久变形，"顶脚"是回弹偏高，先分清再谈换料。
第三句，验证顺序比验证项更贵：定窗口 → 曲线 → 压缩永久变形 → 耐折与低温 → 耐黄变与气味 → 整鞋试穿。
关于我们
"这个件用什么料？"
这是我们被问得最多的一句话，也是最不好一句话回答的一句。因为答案从来不是"用最好的"，是"用最合适的那一档"。
宁波市科隆新材料有限公司，自产改性聚丙烯（PP）造粒，覆盖均聚 / 无规共聚 / 抗冲共聚三档基材，以及填充、玻纤增强、增韧、阻燃、低气味低 VOC、耐候、免喷涂耐划伤等改性方向；兼营各大石化厂 PP 树脂、副牌料与大包料。
运动鞋中底用什么改性PP？答案不是"回弹越高越好"。中底要的是在既定步态与体重区间里，让回弹、缓震、耐久三者落进设计窗口。这篇把性能三角、POE 复配在调什么、八项判据与逐级验证顺序摆清楚，并说明哪三种情况这个件不该用发泡 PP。
- 对照说明：贸易版 87 篇无鞋材板块，本篇无同主题对照篇；差异点在系列内部错开
"鞋中底用什么改性PP，是不是看回弹率就行？"
一个做鞋底配套的技术员这么问我，随后把曲线发了过来。曲线不难看，落球回弹落在偏高的一档。他没说的是，这个件是稳定支撑型，目标人群是大体重慢跑。
鞋中底最容易走偏的地方就在这里：它要的是"按设计曲线回弹"，不是"回弹越高越好"。
同一块中底上，"回弹高"和"缓震好"天生是一对反向指标，想要一头，另一头就得让。回弹堆得太高，卸载时能量快速还给脚，瞬时反馈变尖，穿感就是"顶脚"，稳定性跟着变差。
别的发泡件不是这个逻辑。缓冲垫要的是峰值力低，包装件要的是吸能；鞋中底要的是在某一种步态、某一段体重区间里，回弹与缓震的组合落进设计窗口。
下面按工况、三角、配方、判据、验证五层往下拆。
一、运动鞋中底的工况六维：温度有两头，载荷是反复的
先说结论：鞋中底最特殊的一维是寿命——它不按年份算，按里程和步数算。
| 维度 | 鞋中底的实际工况 | 对材料的要求 |
|---|
| 温度 | 下限常见 −20℃（北方冬季户外）；上限夏季地面与鞋内可到 40-50℃；成品鞋还有仓储存放温度 | 低温不脆裂、低温回弹衰减可控；高温不塌陷 |
| 载荷 | 体重（常见 50-90 kg 级）+ 落地冲击（跑步峰值可达体重的 2-3 倍级）+ 每公里千次级的反复压缩 | 压缩永久变形小、动态疲劳后刚度衰减慢 |
| 介质 | 汗液（偏酸、含盐）、雨水、清洁剂；洗鞋时的浸泡与刷洗 | 耐水解、耐盐、耐清洁剂，不析出不发粘 |
| 寿命 | 按里程算：训练鞋常见按 500-800 km 级的衰减窗口设计；休闲鞋按年 | 衰减曲线要平，不能前 100 km 好、后面塌 |
| 外观 | 白色中底是主流；长期存放与光照后发黄是常见客诉；批次间色差 | 耐黄变、色差可控 |
| 合规 | 鞋材与皮肤接触的相关要求；成品鞋在密闭鞋盒里的气味与 VOC | 配方要过接触与气味两道口径 |
六个维度里最反常识的是寿命。别的件按"用了几年"算，鞋中底按"跑了多少公里"算。客户投诉的原话往往不是"寿命不够"，是"跑三百公里就踩不动了"——这句话里藏着两个指标，第六节拆开讲。
一个内行细节：中底的前掌与后跟衰减速度不一样。后跟载荷高，压缩永久变形累积更快；前掌弯折次数多，是耐折薄弱区。中底很少整块均匀坏掉，而是某一个分区先失效——按整块取样验收，最容易把最差那区测没了。
二、鞋中底的性能三角：回弹、缓震、耐久不可能同时拉满
先说结论：回弹、缓震、耐久是三条互相拉扯的线，同一块中底不可能三条都拉满。
回弹是能量回馈率。跑鞋追求高回弹，因为要"还"能量。但回弹太高有两个代价：卸载时瞬时加速度峰值高，穿感"顶脚"；同密度下泡孔壁更硬，抗压缩疲劳的余地变小。
缓震是冲击吸收，本质是滞后损失：加载与卸载的面积差越大，耗掉的能量越多。缓震好就意味着回弹低，这是一枚硬币的两面。
耐久是压缩永久变形，反复压缩后能不能回到原位。这一项才是真实投诉最主要的来源。
三条线的对拉关系，可以写成一张兑换表。
| 动作 | 回弹 | 缓震 | 耐久 | 其他代价 |
|---|
| 提高发泡倍率（降密度） | 略升 | ↓ | ↓ | 压缩强度与厚度保持同时掉 |
| 提高弹性体（POE）配比 | 先升后平 | ↑ | ↑（适度范围内） | 熔体强度与耐热下降、成本上升 |
| 提高基材结晶度 / 硬度 | ↑ | ↓ | ↑ | 低温更硬、缓震更差 |
| 提高硬段比例 / 交联程度 | ↑ | ↓ | ↑↑ | 工艺窗口变窄、回收性变差 |
文字版结论：最该记住的是第一行和最后一行。降密度是鞋材第一诉求，但它同时扣缓震和耐久；提交联能同时提回弹和耐久，代价落在工艺与回收上。改性PP 中底选型，第一步就是定这三条线的位置关系。
敢否定一个常见做法： 拿"回弹率越高越好"当选型判据，是市场话术，不是工程判据。工程上要的是在这个鞋型的步态与体重区间内，回弹与缓震的组合落进设计窗口——竞速鞋要高回弹低滞后，稳定支撑鞋要缓震优先，用同一张回弹榜去排，必然排错。
还有一条更少人提：低温下弹性体的回弹会下降。温度低，分子链段活动性降下来，模量上升，落地冲击峰值反而更尖（据行业媒体公开资料，B 级）。按常温定的窗口，到 −20℃ 可能整段偏出去——北方冬季的体感差异是真实存在的。
三、发泡 PP 与 POE 复配：POE 在调什么，代价在哪
先说结论：纯 PP 发泡有两个结构性短板，POE 复配各补一半；但 POE 加多了，会反过来伤熔体强度和耐热。
PP 是结晶性聚合物，熔体强度低。发泡时泡孔壁被拉伸减薄，容易被拉破，结果是泡孔不均匀、局部塌陷、并孔。纯 PP 又偏硬，回弹快但缓震差，直接做中底脚感像一块板。
The first thing that POE improves is melt strength and elasticity, so that the cells can hold up during the growth stage. Public journal studies on PP/elastomer foaming show this pattern: the cell density of pure PP foam is about 2.62×10⁶ cells/cm³, with an average cell diameter of about 55.36 μm; after adding 20 wt% elastomer, the cell density increases to about 12.5×10⁶ cells/cm³, and the cell diameter drops to about 25.42 μm (according to public journal data, Grade A). Even when called foamed PP, the cell structure can differ by an order of magnitude—this is why 'two suppliers both report foamed PP, but the feel underfoot is completely different.'
The second thing POE addresses is reducing stiffness and improving cushioning. Using modified PP as the foamed substrate with POE blending is the current mainstream approach.
There are three costs. First is compatibility: the POE main chain is polyethylene-based and has limited compatibility with PP, requiring compatibilization (commonly used in public journals is PP-g-MAH, grade A). Second, adding too much will weaken the continuous phase framework: public patents indicate that at low content, rebound improvement is not obvious; at high content, the framework weakens, heat resistance decreases, and it is prone to shrinkage and collapse during foaming. The preferred mass ratio is PP to α-olefin elastomer = (50-75):(25-50) (grade A). Third is cost—POE unit price is higher than PP.
Text version conclusion: POE is a tool for 'adjusting time constants and stiffness,' and the amount is determined together by three factors: permanent compression deformation, rebound speed, and lower limit of rigidity. The ceiling is not set by the formulators; it is determined by the minimum stiffness that this shoe type can accept.
The layer of foaming process also needs to be distinguished first. Physical foaming (supercritical CO₂/N₂) uses gas as the foaming agent. The critical parameters of supercritical CO₂ are about 31.1℃/7.38 MPa (public physical constants), resulting in finer and more uniform pores with no chemical residues. Chemical foaming (AC type) has a simple process and low cost, but at the expense of decomposition residues and odor. The mainstream trend for high-end midsoles is physical foaming, while ordinary midsoles still use chemical foaming extensively—this is a division of labor, not a matter of superiority or inferiority. As for specific process parameters (saturation temperature, pressure, gas content, depressurization rate), they must be confirmed through actual measurement according to the equipment and formula.
4. Comparison of Material Routes: Division of Labor Boundaries between Foamed PP and EVA, PU, PEBA, TPEE
Let's start with the conclusion: These approaches are not addressing the same type of problem — they are categorized by 'what problem they solve,' not by 'who is better.'
| Route / Material | Get what | Cost / Boundary |
|---|
| Foamed PP (bead type, EPP system) | Low density, medium to high resilience, good resistance to compressive fatigue, dimensional stability; PP is a thermoplastic system, and waste material can theoretically be remelted and processed | Low melt strength requires formula adjustment; stiffness is relatively high, cushioning is average; narrow foaming window |
| PP POE Blended Foaming (Main Theme of This Article) | The pores are finer and more uniform, stiffness decreases, cushioning is improved, and low-temperature toughness is better | Needs capacity increase; adding more improves melt strength and heat resistance; cost rises |
| EVA (including POE-EVA blends) | The most mature process, low cost, soft, mainstream for casual shoes | Rebound and durability are weaknesses, long-term wear easily 'flattens' them (according to publicly available industry media information, grade B) |
| PU / Supercritical PU | Balanced resilience and durability, with good performance in compressive permanent deformation | At the same magnification, the density is higher and the foot feel is firmer; the residue and recovery of the cross-linked system is another matter. |
| PEBA (Nylon Elastomer) | Lower density, higher energy feedback, and wider temperature range at the same magnification | High cost, a common approach is to blend with EVA/TPU to reduce costs |
| TPEE / TPU pellets | Balanced durability and resilience, both bead and sheet material processes are mature | Density and foot feel are relatively solid; upstream processes are highly concentrated |
| Rubber substrate (vulcanization system) | Wear-resistant, grippy, durable | High density, low resilience, mostly used for outsoles rather than midsoles |
Text version conclusion: EVA and PU are the mainstream domestic shoe materials, while modified PP-based systems are later entrants, relying on 'lighter weight, thermoplastic recyclability, and compression fatigue resistance.' Route selection first answers the question: which of these characteristics is the most critical for this part? For rebound priority, look at PEBA/supercritical systems; for cost and softness, look at EVA; for light weight and recyclability, look at modified PP-based systems; for balanced durability, look at PU/TPU.
5. ★ Selection Criteria Table: Seven indicators for sneaker midsoles, each with a verification method
Conclusion first: The column to look at first in this table is the third one — the difficulty with shoe midsoles is not 'which indicator to look at,' but 'which set of shoe measurement methods to use.'
| Indicator | Threshold Value (Typical) | Verification Method · Standard Number | Common Failures | Common solution |
|---|
| Apparent Density | Determine the window according to the shoe type; publicly disclosed industry media data: EVA-based 0.08-0.12 g/cm³, PEBA-based 0.07-0.10, TPU-based 0.05-0.13 (Grade B, cannot be directly compared due to different calibrations) | GB/T 6343 | Density increases → overweight; decreases → both compressive strength and durability drop | Set windows according to the 'density-performance' curve, not following a single low density value |
| Ball rebound rate | Set the window according to the shoe type; in public data, the PEBA sheet was measured at about 73-76% (Grade B, needs to be cross-checked with the original text) | GB/T 6670-2008 (φ16 mm/16 g steel ball, 500 mm drop height, sample conditioned ≥24 h, measured 3 times and averaged) | Too high → foot pressure, poor stability; Too low → loss of power | Use POE formulation and pore structure to capture the rebound into the window |
| Compression set | Determine according to the cycle and temperature specifications; according to public information, a certain type of sheet reports 18-23% (Grade B) under (50%/6 h/50℃) | GB/T 6669-2008 (Compressed to 50% or 75%, 70°C × 22 h, recovery 30 min to test residual deformation) | After running a few hundred kilometers, 'cannot step' and loss of thickness and preload | Elastomer ratio Pore refinement Adjust together with substrate grade |
| Size and batch are consistent | Determine according to the fitting line and assembly tolerance; density and size are linked quantities, and batch density fluctuations must have an upper limit. | Density is checked batch by batch according to GB/T 6343; dimensions are fully inspected according to the drawing specifications. | Adheres to yield fluctuation, thickness out of specification | Density Control Window Batch Data Card |
| Durable | Verify according to the method for the whole shoe or outsole flex resistance; the standard does not include items with a heel height >70 mm or a thickness at the bending part >25 mm. | GB/T 3903.1-2017 'Footwear — Whole Shoe Test Methods — Flexing Performance' | Cracking at the flexion area of the forefoot, rupture of the blister wall | Increase elastomer proportion, optimize forefoot density |
| Low-temperature performance | Based on the minimum operating temperature; rebound decreases at low temperatures, modulus increases, and the impact peak becomes sharper (Grade B) | Bending after low-temperature pre-treatment according to GB/T 3903.1-2017, comparison of low-temperature rebound | Hardening and cracking in winter | Choose base materials or elastomer systems that perform better at low temperatures |
| Yellowing Resistance and Odor | Common acceptance for yellowing grade ≥3-4 (Grade B, subject to customer acceptance documents); odor is based on customer criteria, VDA 270 odor ≤3 can be used as supporting evidence (not national standard) | Yellowing is measured according to HG/T 3689-2014 (Method A: solar lamp method / Method B: UV lamp tube method; chamber temperature 50±2℃, humidity 65±5%, colorimetry within 30 minutes after illumination); odor is measured according to VDA 270 | White midsoles turn yellow after long-term storage or exposure to light; strong odor when unpacked | Antioxidant system, avoid additives that easily cause yellowing; use less chemical foaming agent, control release agents and low-molecular-weight additives |
Text version of the conclusion: Among the seven items, compressive permanent deformation and yellowing resistance are the most likely to be ranked last — the former is close to real complaints, the latter is unrelated to 'performance' but most crucial. Consider this table as a medical examination report; missing one item means it is not deemed qualified.
6. Common Failures and Root Causes: Four phenomena in the shoe midsole, four root causes
Conclusion first: Among the four types of failures, only one is due to 'wrong material,' while the other three are related to the target window, the additive system, and the sampling method.
Failure 1: 'After running 300 kilometers, it can't be pressed down.' The customer says 'it has stiffened,' which essentially means the pore structure has collapsed, causing permanent compression deformation — the thickness cannot return, and the preload is lost. The criterion lies in permanent compression deformation (GB/T 6669 standard), not in the rebound rate. Using the rebound rate to explain this phenomenon is wrong from the very beginning.
Failure 2: Saying 'too tight on the foot' as soon as you put it on. This is not due to insufficient rebound; on the contrary, the rebound is too high and the hysteresis loss is too small — first, look at the design window of this shoe model, don’t rush to switch to softer materials.
Failure 3: Yellowing of the white midsole. It is unrelated to performance but can be commercially critical. First, examine the additive system (antioxidants and components prone to yellowing), then look at the foaming process—the residues from chemical foaming accelerate yellowing. Determination is according to HG/T 3689-2014, with color measurement within 30 minutes after exposure to light; results beyond this time are not valid.
Failure Four (Dare to challenge a common practice): Using a whole midsole sample to test performance. Midsoles rarely fail evenly—heel compression deformation accumulates quickly, and the forefoot bears heavy bending stress. Sampling the whole piece only gives an average, while complaints always arise in the worst-performing section. The correct approach is to sample by forefoot/midfoot/heel sections and set thresholds for each section.
7. Verification sequence: What to verify first and what to verify later in the shoe midsole
Conclusion first: The most expensive failure of the shoe midsole happened during the whole shoe stage, and its root cause happened to be in the first two steps that weren't done.
| Order | Verification item | However, just the criteria for returning |
|---|
| ① Determine Shoe Style and Target Window | Gait type, weight range, target density, and rebound/cushioning window | The window is not set, all subsequent thresholds are guesses → go back and ask again |
| ② Density and Compression-Rebound Curve | Density (GB/T 6343) Rebound of falling ball (GB/T 6670) Compressive stress-strain curve | The curve cannot fit into the window → Revert to the elastomer ratio and density settings |
| ③ Compressive permanent deformation | GB/T 6669 Caliber (50% or 75%, 70℃×22 h, recovery 30 min), sampled according to zones | Residual deformation exceeds threshold → Revert to bubble pore structure and mix ratio |
| ④ Resistance to folding and low temperatures | GB/T 3903.1-2017 Bending Bending after low-temperature pretreatment Comparison of low-temperature springback | Cracking at the flexing area or excessive low-temperature rebound decay → Return to the substrate and elastomer |
| ⑤ Resistance to yellowing and odor | HG/T 3689-2014 (Method A/B); odor is verified according to VDA 270 specifications | Yellowing does not reach the threshold, odor exceeds standard → Return to additives and foaming route |
| ⑥ Full Shoe Fitting and Durability | Test wear and dynamic fatigue based on mileage/frequency, and see if the attenuation curve is smooth | Decay curve steep → Return to ① Reset window |
Text version of the conclusion: The sequence is fixed window → curve → compression set → folding and low temperature → yellowing resistance and odor → whole shoe fitting. Compression set must be done before the whole shoe; it is most likely to veto an item and is closest to the original complaint wording.
8. Reverse Honesty: In these three situations, the midsole of the shoe should not use foamed modified PP.
Conclusion first: As long as 'things that the foamed parts can't reach' appear, you shouldn't force it.
First, it requires extremely high rebound energy feedback. The energy return target for racing shoe midsoles is generally set above 80%, and higher-end systems report above 85% (according to brand claims, with varying testing standards, so they cannot be directly compared). The ceiling for modified PP-based foaming systems is not in the same place. One should opt for high-rebound systems like PEBA, supercritical PU, or TPEE, or use a dual-density design to assign the high-rebound layer to other materials.
Second, it requires almost no attenuation under long-term high-intensity use. The intensity of professional competition use would push the permanent compression deformation to its limit. The attenuation of foamed porous materials is physical, and modification can only flatten the curve, not eliminate it. One should go for systems like PU/TPU that have more stable rebound, or have the structure (such as propulsion boards) share the attenuation.
Third, an extremely high density accuracy is required. The automated bonding line is very sensitive to fluctuations in density and thickness. The density and size of the foamed part are interlinked—if the density changes, the size follows, and batch-to-batch density fluctuations will directly affect the yield of this line. It is necessary to first confirm the batch fluctuation range of the foaming line, or switch to a non-foaming system with more stable density.
9. Material Change Risk List: What to Examine First When Changing Foamed PP Midsole Material
Before deciding to try foaming PP, go through this chart first. The customer's real concern is often not performance, but 'whether I need to modify my current mold and process'.
| Items to move | What needs to be confirmed | What will happen if I don't do it? |
|---|
| Forming process route | Bead kettle pressing / sheet molding / blank molding expansion / continuous extrusion, the equipment and cycle times of the four routes are completely different | Chose a route that can't be handled, the sample can't be made at all |
| Contraction and Density | Density is linked with size, not a fixed value; which density is the mold reference calibrated to? | The dimensions and thickness do not match |
| Material Temperature and Mold Temperature/Steam Conditions | The pore structure and sintering quality are sensitive to temperature, time, and pressure. | Pore coarsening, poor sintering, local collapse |
| Demolding and Release Agents | Use should be controlled; avoid using it if possible. Residue can harm both the scent and cleanliness. | Odor and excessive precipitation |
| Color difference | The white midsole must first have the color swatch confirmed, and then undergo yellowing resistance verification. | Batch color difference dispute |
| Verification order | Set window → Curve → Compressive permanent deformation → Flexibility and low temperature resistance → Yellowing and odor resistance → Whole shoe fitting | All the risks are concentrated to explode at the complete shoe stage |
Text version conclusion: Changing materials affects three areas: the molding process, the process window, and color difference. The one that should be discussed first is the verification sequence. Skipping curves and going straight to the whole shoe is equivalent to leaving the most expensive failure until the end.
10. One-page report comparison table: Midsole selection for shoes can be directly pasted into the PPT
Let's start with the conclusion: there is only one criterion—whether the client can use this table to finalize the material direction in a single meeting.
| Scene | Recommended Route | Key indicators | Verification Standard | Conditions that need to be confirmed first |
|---|
| Midsole of everyday training shoes | PP POE blended foaming, density determined according to shoe type | The ball bounces back into the window, and compression causes permanent deformation, leaving a margin | GB/T 6670, GB/T 6669 | Target weight range, gait type |
| Stability Support / Cushioning Priority | Rebound directed toward the lower edge of the window, prioritize shock absorption | Compression-rebound curve is relatively gentle; zoned hardness | GB/T 6670 Compressive Stress-Strain Curve | Supporting structure design, zoning hardness definition |
| Northern winter style | Substrate or elastomer system with better low-temperature performance | Low-temperature rebound decay No cracking at low-temperature bending | GB/T 3903.1-2017 Low-Temperature Rebound Comparison | Record of the lowest local temperature |
| White appearance model | Physical foaming route Anti-yellowing system | Yellowing level reaches the customer's threshold | HG/T 3689-2014 (Method A/B) | Customer yellowing threshold, storage period |
Text version conclusion: The purpose of this table is to allow technicians to report conclusions directly. Do not squeeze the rebound, cushioning, and durability lines all into the phrase 'good performance'—each of the three should have its own window.
Eleven, the part that most easily goes wrong on this item is often not the rebound.
The two most common types of midsole failures in shoes are 'too hard to step' and 'toe push,' neither of which is caused by 'insufficient rebound.' 'Too hard to step' corresponds to compression set (GB/T 6669 standard); 'toe push' corresponds to high rebound and low hysteresis loss (GB/T 6670's ball drop rebound and compression–rebound curve window).
Many conclusions that 'the material doesn't work' ultimately turn out to be due to the window being set incorrectly, or because the sampling took an average of the whole piece, missing the worst area. The common practice in the industry is to set the substrate grade, the elastomer (POE) ratio, and the foaming process together—looking at any single item alone is meaningless. The key is whether the substrate grade, elastomer ratio, foaming process, and density window can all match simultaneously.
Ningbo Kolon New Materials Co., Ltd. commonly supplies modified polypropylene (PP) particles as the foaming substrate for this component: providing recommendations for the substrate grade and POE blending ratio according to the target window, and suggesting low-odor, anti-yellowing additives based on shoe type and process route. The main issues addressed are 'unable to adjust the curve into the window' and 'degradation after a short run.' Formulations can be adjusted according to working conditions and can be used in small-sample comparisons and trial molding.
Frequently Asked Questions
Question: Is a higher rebound rate better?
Answer: No. High rebound means that energy is returned quickly when unloading, the feedback is sharper, it feels like it 'presses on the foot', and stability is also poor. What is needed is to fall within the window of this shoe model.
Q: If you add a bit more POE, won't both cushioning and rebound improve?
Answer: Adding an excessive amount comes with two costs: limited compatibility between POE and PP, requiring increased capacity; if too much is added, the skeleton becomes weaker, heat resistance decreases, and it is more prone to collapse during foaming; another cost is the price. The upper limit is determined by the minimum stiffness that this shoe model can accept.
Question: Is physical foaming necessarily better than chemical foaming?
Answer: No. Physical foaming has no chemical residues and produces finer and more uniform pores, but the cost is higher equipment and process control requirements; chemical foaming is simpler and cheaper, but the trade-off is residues and odor. Division of labor is based on product positioning.
| Operating condition | Key criterion | Regular supply |
|---|
| Midsole of everyday training shoes | Ball rebound (GB/T 6670) drop window, permanent deformation under compression (GB/T 6669) reserve | Modified PP foam substrate POE blending direction |
| Stable Support / Shock Absorption Priority | Compression-rebound curve is relatively gentle shock, zoned hardness | Foaming substrate Elastomer ratio adjustment |
| White appearance model | Yellowing Grade (HG/T 3689-2014) | Low-odor, anti-yellowing additive direction |
Finally, three sentences. The first sentence: what is required of the shoe midsole is 'rebound according to the design curve,' not 'the higher the rebound, the better'—only two of the three lines can be maximized at the same time.
In the second sentence, '踩不动' refers to compression set, and '顶脚' refers to overly high rebound; first clarify the difference before discussing material replacement.
Third sentence, the verification sequence is more expensive than the verification items: setting the window → curve → compression permanent deformation → fold resistance and low temperature → yellowing and odor resistance → whole shoe fitting.
About Us
What material is this piece made of?
This is the question we are asked the most, and it is also the hardest one to answer. Because the answer is never 'use the best,' but 'use the one that is most suitable for the situation.'
Ningbo Cologne New Materials Co., Ltd. produces modified polypropylene (PP) granules, covering homopolymer, random copolymer, and block copolymer base materials, as well as modifications including filled, glass fiber reinforced, toughened, flame-retardant, low odor and low VOC, weather-resistant, and scratch-resistant without coating; it also deals in PP resins from major petrochemical plants, off-spec materials, and bulk materials.
