去年秋天，一个做运动鞋的客户拿着两块中底样片来找我们，一开口就报了个数："回弹率要 70 以上，密度要能压到 0.15。"
我说这两个数可以同时达到，但你先回答我一个问题：这双鞋卖给谁、打算穿多久？
他愣了一下。因为鞋中底材料真正的分水岭，不在"刚穿上多弹"，在"穿三个月还弹不弹"。这篇就把中底材料的选材逻辑讲清楚。
一、中底比的不是回弹，是"回弹能撑多久"
先说清中底在鞋里做什么。
中底夹在大底和鞋垫之间，承担三件事：缓冲落地冲击、回馈蹬地能量、维持鞋型。
前两件是"穿上去的感受"，第三件是"穿三个月后的感受"。
消费者投诉最多的问题，恰恰是第三件——鞋穿一阵子就"塌了"，踩着发硬，走路累。这个现象有个专业名字：压缩永久变形。
它的意思是：材料被反复压之后，回不到原来的厚度了。
回弹率是一个瞬时指标，压缩永久变形是一个长期指标。两个都测，但后者更接近真实体验。
一句话：中底选材，瞬时的回弹率决定"卖点"，长期的压缩永久变形决定"复购"。
二、三条材料路线，并列看代价
| 路线 | 回弹（瞬时） | 回弹保持（长期） | 密度 | 成本 | 适合定位 |
|---|
| EVA 发泡（传统） | 中 | 中到弱 | 低 | 低 | 大众跑鞋、休闲鞋 |
| TPAE / PEBA 尼龙弹性体 | 高 | 好 | 低 | 中高到高 | 中高端跑鞋、竞速鞋 |
| TPU 发泡 / 其他弹性体 | 中高 | 好 | 中 | 中 | 训练鞋、大底结合件 |
看这张表，重点不在"哪个更弹"，在回弹保持那一列的代价。
EVA 便宜、成熟、发泡工艺简单，是绝大多数鞋在用。但 EVA 的问题是回弹衰减快——穿一段时间，泡孔结构疲劳，回弹下降明显。
TPAE 和 PEBA 属于尼龙弹性体（聚醚嵌段酰胺），分子里有硬段和软段：硬段提供强度和回弹，软段提供柔顺。这个结构让它在反复压缩下能恢复得更好，所以"穿三个月还弹"这件事它做得更好。
代价是单价高，而且加工窗口比 EVA 窄。
这里有一条要提醒的：尼龙弹性体不是"更强的 EVA"，它是另一套体系。发泡工艺、模具、回收路径都不同，不是换个料就能上。
三、工况六维：中底被什么夹住
力学：压缩循环。 每一步都是一次压缩。一双鞋跑 500 公里，就是几十万次压缩循环。这是典型的高周压缩疲劳。
温度。 这一维最容易被漏。低温下弹性体的回弹会明显下降——冬天跑步鞋变硬，不只是感觉，是材料特性。寒冷地区的鞋必须按最低使用温度考核。
环境：紫外与湿气。 浅色中底暴露在紫外下会黄变，湿气会加速水解。户外鞋尤其要考核。
外观。 中底是外露件，颜色、纹理、有无黄变都影响销售。
寿命。 这里的"寿命"是鞋的服役期，通常按里程或月份算。
合规。 接触皮肤、部分接触地面，材料安全与挥发物要求要按消费品法规处理。
六维里最容易被忽略的是"温度"和"环境"两条的叠加。
低温加湿气，弹性体的表现会比单看一条差。
验收方案要把这两条放在一起跑，不能分着跑。
四、选型判据表（这是本篇最该收藏的一页）
门限值是方向性建议，不是验收标准——实际数值必须由你的定位、成本和工艺实测确定。
| 指标 | 方向性门限 | 验证方法 / 标准 | 常见失效 | 通行解法 | 对应助剂体系 |
|---|
| 回弹率 | 按定位定，竞速类要求更高 | GB/T 1681（回弹性） | 脚感变硬 | 选高回弹弹性体 | — |
| 压缩永久变形 | 按服役期目标定，越小越好 | GB/T 7759 | 中底塌陷、鞋型走样 | 提高回弹保持体系 | 交联 / 结晶调控助剂 |
| 密度 | 按轻量目标定 | GB/T 533 | 重量超标 | 超临界发泡工艺 | 成核剂（泡孔均匀性） |
| 低温回弹 | 覆盖最低使用温度 | 低温回弹测试 | 冬天变硬、开裂 | 选低温性能好的软段 | — |
| 耐黄变 | 按外观要求定 | 紫外老化 + 色差 | 浅色中底发黄 | 抗黄变体系 | 光稳定剂 / 抗氧剂 |
| 水解稳定性 | 湿热条件下性能保留 | 湿热老化实测 | 长期存放后变脆 | 耐水解体系 | 抗水解剂 |
| 挥发与气味 | 按消费品要求定 | 场景规定方法 | 开箱异味 | 选低挥发体系 | — |
怎么用这张表：先看第二行"压缩永久变形"。中底的差评大多来自这里。回弹率可以靠配方和工艺做高，但如果回弹保持不行，穿一个季度就现原形。
五、六种常见失效，和它们真正的根因
失效一：穿两三个月后中底塌了、踩着发硬。
根因是压缩永久变形。泡孔结构在反复压缩下疲劳，回不到原厚度。解法是提高回弹保持能力——选更高比例的弹性恢复体系，而不是单纯提高密度。
失效二：浅色中底穿一段时间发黄。
根因是光氧老化。浅色件对光稳定要求更高，但这不只是"加光稳定剂"的问题——基材本身的耐黄变基础很重要。看到发黄，先分清是表面发黄还是整体发黄，处理方向不同。
失效三：冬天鞋变硬、低温下有裂纹。
根因是低温回弹下降。软段的玻璃化转变温度决定了这个行为。要按实际使用的最低温度选软段，不能拿常温数据说话。
失效四：同一批中底密度不均、脚感不一致。
这多半是发泡工艺或成核分散的问题。泡孔均匀性与成核剂的分散直接相关——成核剂分散不均，泡孔大小就有差异，密度和回弹都会散。看到这个现象，先查发泡工艺和成核体系，别急着换基料。
这里有一条要直说的：中底的失效排查，先分"瞬时指标没达到"还是"长期指标衰减"，这两类的解法完全不同。 前者靠配方，后者靠体系和结构。
六、加工与验证：几件必须提前定的事
干燥。 尼龙弹性体含酰胺段，吸湿是必须处理的。料在包装里受潮会直接影响发泡与性能，干燥窗口按实测含水率定。
发泡工艺的匹配。 超临界发泡对材料熔体强度有要求。同一款料，在不同发泡工艺下表现可能完全不同，工艺和材料要一起开发，不能分开选。
模具与收缩。 中底是厚壁异形件，收缩不均。模具的补偿要按件做。
仓储与运输。 中底是半成品，厂内和卖场各存一段。
湿度高会加速水解，强光会让浅色件提前黄。
包装和仓储条件要写进作业要求。
很多"料不行"的结论，追下去是仓库的问题。
贴合与后加工。 中底要和大底、鞋面贴合，胶和处理剂要一起选。
料面析出会让贴合失效，这一条要和助剂体系一起看。
贴不牢的鞋，返修成本比换料高。
发泡还有一个常被忽略的变量：模具温度分布。
模温不均，泡孔就一边大一边小，同一只鞋两侧的脚感都不同。
先测模温分布，再调发泡参数。
这一步在鞋厂常被跳过，却是成本偏低的一次改善。
泡孔的一致性，一半靠料，一半靠模温。
验证顺序。 建议这样排，顺序不要换：
1. 材料级：回弹、压缩永久变形、密度、低温回弹
2. 样片级：不同发泡条件下的样片对比
3. 成品级：整只中底的密度分布、几何尺寸
4. 疲劳级：模拟压缩循环，中途复测回弹
5. 环境叠加：低温 + 湿热 + 紫外
顺序不能换。 前一关不过就往下走，后面的数据没有解释意义。
七、边界：什么时候这事不该谈
以下四种情况，这个件走尼龙弹性体不建议推进：
其一，纯大众款、单价卡得很紧的鞋。 尼龙弹性体的成本是 EVA 的数倍。用在中底上，只有定位够高才回收得回来。
其二，没有配套发泡工艺能力的产线。 尼龙弹性体不是换个料就能用，要匹配熔体强度和发泡窗口。没有工艺支撑，好料也做不出好中底。
其三，使用环境长期低于材料的低温适用范围。 到了那个温度，弹性体的回弹和韧性都不够，要看其他体系。
其四，用量小到摊不平工艺开发成本。 中底的材料验证是"材料 + 工艺"一起做的，投入不小。
其五，只做一次性或短周期使用的鞋。 这类鞋的寿命撑不到体现回弹保持优势的阶段，
用高成本体系是浪费，EVA 更合适。
其六，产线没有烘干与湿度控制条件。 尼龙弹性体吸湿敏感，
没有烘干和车间湿度控制，批次稳定性做不好，先补条件再谈换料。
把这六条写在前面，不是劝退，是省时间。
八、两套账分开算：一张对照表
不按材料分，改按"什么时候看什么"分，反而更清楚。
| 看什么 | 什么时候看 | 怎么测 | 谁最在意 |
|---|
| 瞬时回弹 | 选料、打样、提炼卖点 | 回弹率测试 | 产品与市场 |
| 回弹保持 | 定服役期、定是否换料 | 压缩永久变形 + 疲劳 | 品质与售后 |
| 低温回弹 | 定销售区域与季节 | 低温回弹测试 | 产品与区域 |
| 泡孔均匀性 | 定工艺窗口 | 切片显微观察 | 制造与工艺 |
这张表最该带走的不是指标名字，是"什么时候看"那一列。
选料阶段只看瞬时回弹，等于把售后的问题留到售后。
该在选料阶段测的项，别拖到出货之后。
还有一句：这四项的优先级，是随定位变的。
大众款优先控成本，竞速款优先控回弹保持。
先定定位，再定优先级，顺序不能倒。
换料风险清单（从 EVA 换到尼龙弹性体中底，要动的东西）
| 环节 | 要动什么 | 容易漏的点 |
|---|
| 模具 | 收缩与冷却行为不同，基本要重开或大改 | 沿用 EVA 模的收缩率 |
| 干燥 | 尼龙弹性体要烘干，按含水率定窗口 | 沿用 EVA 不烘的习惯 |
| 工艺 | 发泡窗口与熔体强度要重新匹配 | 沿用 EVA 的发泡参数 |
| 料温 / 模温 | 加工窗口比 EVA 窄，要重新定 | 只按供应商推荐值给 |
| 脱模与后处理 | 冷却定型方式可能不同 | 沿用原有冷却时间 |
| 色差 | 体系不同，色板要重新确认 | 浅色件的黄变标准要另定 |
| 验证顺序 | 材料 → 样片 → 成品 → 疲劳 → 环境 | 只做静态测试 |
一页纸汇报表（给要向上汇报的人）
`
项目：鞋中底 · 材料路线评估
结论方向：尼龙弹性体（TPAE / PEBA）可作为中高端定位的候选路线
一、必须守住的三条
1. 回弹率与压缩永久变形要一起测，后者权重更高
2. 低温回弹按实际使用温度考核
3. 材料与发泡工艺必须一起开发
二、前置条件（任一不满足则建议暂缓）
· 产品定位能承载材料成本
· 有匹配的发泡工艺能力
· 使用环境最低温在体系范围内
· 有疲劳与老化验证的周期预算
三、下一步动作
1. 取现有中底，测压缩永久变形衰减曲线
2. 按实际最低温做回弹对比
3. 小批试发泡，看密度与泡孔均匀性
风险提示：本路线的主要不确定性在长期回弹保持与工艺匹配，不在初始回弹率。
`
读者常问的两句
问：TPAE 和 PEBA 是不是一回事？
都属尼龙弹性体大类，都是聚醚嵌段酰胺结构，但硬段与软段的搭配不同，性能倾向就不同：有的偏回弹，有的偏低温，有的偏耐温。不能笼统说"尼龙弹性体"，要落到具体型号的软硬段结构上去问。
问：中底是不是密度越低越好？
轻量是目标，但不是越低越好。密度太低，压缩永久变形和回弹保持都会变差，穿不久就塌。轻量、回弹、耐用这三件事，本质上有取舍。
结语
鞋中底材料的选材，说到底是一道长期保持题，不是瞬时手感题。
判断链只有三条：
定位定成本上限 → 服役期定回弹保持 → 使用环境定温度边界。
三条都定完，"用什么材料"这个问题自然就有答案了。
如果你手上正有一个中底项目要定料，把三样东西发过来就能给方向：目标定位、预计服役里程或月份、最低使用温度。
补一句：中底这件事，验证的钱基本花在"时间"上。
压缩疲劳和老化都要跑周期，先排期，再谈价格。
站在树脂厂和注塑厂之间，中底这件事其实一半的答案已经写好了——写在消费者的里程表上，不写在物性表上。
我们做的事很具体：把 PA6、PA66、PA46、PA11、PA12、PA6T、PA9T 和尼龙合金这些树脂，改成某个件真正能用的样子；顺带做改性 PPO、PPS 和热塑性弹性体。
也经营各大化工巨头的尼龙树脂、副牌料和大包料，另长期收尼龙原料、水口回料与各类尼龙废料，有正规处置渠道。
这类件的选料与试模，可以一起聊。
Last fall, a client who makes sneakers came to us with two midsole samples, and as soon as he spoke, he quoted some numbers: 'The rebound rate must be above 70, and the density must be able to be pressed to 0.15.'
I said these two numbers can be reached at the same time, but first answer me a question: who are these shoes being sold to, and how long do you plan to wear them?
He was momentarily stunned. Because the real turning point of the midsole material is not about 'how bouncy it feels when first worn,' but about 'whether it still bounces after three months of wearing.' This article will clarify the logic behind the selection of midsole materials.
1. Midsole is not about rebound, but how long the 'rebound can last'
First, let's clarify what the midsole does in a shoe.
The midsole is sandwiched between the outsole and the insole, performing three functions: cushioning landing impact, returning energy during push-off, and maintaining the shoe's shape.
The first two are the 'feel when you put it on,' and the third is the 'feel after wearing it for three months.'
The issue consumers complain about the most is precisely the third one—the shoes 'collapse' after being worn for a while, feel stiff when stepping on them, and make walking tiring. This phenomenon has a technical name: permanent compression deformation.
It means that after the material is repeatedly compressed, it cannot return to its original thickness.
Rebound rate is an instantaneous indicator, while compression permanent deformation is a long-term indicator. Both are measured, but the latter is closer to the real experience.
In a nutshell: The choice of midsole material and its instantaneous rebound rate determine the 'selling point,' while its long-term compression and permanent deformation determine 'repurchase'.
Two or three material routes, compare the costs side by side
| Route | Rebound (Instantaneous) | Rebound retention (long-term) | Density | Cost | Suitable for positioning |
|---|
| EVA Foam (Traditional) | middle | Medium to weak | Low | Low | Mass-market running shoes, casual shoes |
| TPAE / PEBA Nylon Elastomer | Tall | Good | Low | Medium-high to high | Mid-to-high-end running shoes, racing shoes |
| TPU Foaming / Other Elastomers | Medium-high | Good | middle | middle | Training shoes, outsole connectors |
Looking at this table, the focus is not on 'which is more bouncy,' but on the cost in the column for rebound maintenance.
EVA is cheap, mature, and has a simple foaming process, and is used in the vast majority of shoes. But the problem with EVA is rapid rebound decay — after wearing for a period of time, the foam structure fatigues, and the rebound decreases significantly.
TPAE and PEBA belong to nylon elastomers (polyether block amides), with hard and soft segments in their molecules: the hard segments provide strength and resilience, while the soft segments provide flexibility. This structure allows them to recover better under repeated compression, so the fact that they can 'stay resilient even after three months of wear' is something they do better.
The cost is a high unit price, and the processing window is narrower than EVA.
Here is a reminder: Nylon elastomer is not a 'stronger EVA'; it is a completely different system. The foaming process, molds, and recycling paths are all different, and you can't just switch the material and use it.
3. Six-dimensional working condition: What is pinching the midsole
Mechanics: compression cycles. Each step is a compression. Running 500 kilometers in a pair of shoes means hundreds of thousands of compression cycles. This is typical high-cycle compression fatigue.
Temperature. This dimension is the easiest to overlook. The rebound of elastomers decreases significantly at low temperatures—running shoes become stiff in winter, and this is not just a feeling, it's a material property. Shoes in cold regions must be evaluated based on the minimum usage temperature.
Environment: UV and moisture. Light-colored midsoles exposed to UV will yellow, and moisture will accelerate hydrolysis. Outdoor shoes especially need to be evaluated.
Appearance. The midsole is an exposed part; its color, texture, and whether it yellows all affect sales.
Lifespan. Here, 'lifespan' refers to the service life of the shoes, usually calculated by mileage or months.
Compliant. For contact with skin and partial contact with the ground, material safety and volatile substance requirements must be handled according to consumer goods regulations.
The easiest to overlook among the six dimensions is the combination of 'temperature' and 'environment'.
In a low-temperature humid environment, the performance of the elastomer will be worse than when looking at a single sample.
The acceptance test plan should run these two items together, not separately.
4. Selection Criteria Table (This is the page you should collect the most in this article)
Threshold values are directional recommendations, not acceptance standards—the actual numbers must be determined by your positioning, costs, and process measurements.
| Indicator | Directional Threshold | Verification Method / Standard | Common Failures | Common solution | Corresponding auxiliary system |
|---|
| Rebound rate | Set according to positioning; racing types require higher standards | GB/T 1681 (Rebound Resilience) | The foot feel has become harder | Choose high-rebound elastomer | — |
| Compression set | Set according to the service period target, the smaller the better. | GB/T 7759 | Midsole collapse, shoe shape deformation | Enhance the rebound retention system | Crosslinking / Crystallization Control Additive |
| Density | Set according to lightweight goals | GB/T 533 | Overweight | Supercritical foaming process | Nucleating agent (pore uniformity) |
| Low-temperature rebound | Covers the minimum operating temperature | Low-temperature rebound test | Hardening and cracking in winter | Choose soft segments with good low-temperature performance | — |
| Yellowing resistance | Determined according to appearance requirements | UV Aging Color Difference | The light-colored midsole is yellowing | Anti-yellowing system | Light Stabilizer / Antioxidant |
| Hydrolytic stability | Performance retention under humid and hot conditions | Actual measurement of damp-heat aging | Became brittle after long-term storage | Hydrolysis-resistant system | Anti-hydrolytic agent |
| Volatility and Odor | Set according to consumer goods requirements | Scene specification method | Unboxing odor | Choose a low volatility system | — |
How to use this table: first look at the second row 'compression set'. Most of the negative reviews of the midsole come from here. The rebound rate can be increased through formulation and process, but if the rebound is not maintained, it will show its true performance after wearing for a season.
Five or six common failures and their real root causes
Failure 1: After wearing for two to three months, the midsole collapsed and felt hard when stepped on.
The root cause is compression set. The cellular structure fatigues under repeated compression and does not return to its original thickness. The solution is to improve the ability to retain resilience — choose a system with a higher proportion of elastic recovery, rather than simply increasing density.
Failure 2: Light-colored midsoles turn yellow after wearing for a period of time.
The root cause is photo-oxygen aging. Light-colored parts require higher light stability, but this is not just a matter of "adding light stabilizers"—the substrate's resistance to yellowing is very important. When yellowing occurs, first distinguish whether it is surface yellowing or overall yellowing, and the treatment direction is different.
Failure three: Shoes become hard in winter and develop cracks at low temperatures.
The root cause is the decrease in low-temperature rebound. The glass transition temperature of the soft segment determines this behavior. The soft segment should be chosen based on the lowest temperature in actual use, not based on room temperature data.
Failure 4: Inconsistent midsole density and feel within the same batch.
This is mostly an issue with the foaming process or nucleating dispersion. The uniformity of the pores is directly related to the dispersion of the nucleating agent—if the nucleating agent is unevenly dispersed, the pore sizes will vary, and the density and resilience will be inconsistent. When you see this phenomenon, first check the foaming process and nucleating system, and don't rush to change the base material.
Here's something that needs to be said directly: for midsole failure troubleshooting, first distinguish between 'instantaneous indicators not met' and 'long-term indicator degradation'; the solutions for these two types are completely different. The former relies on the formulation, while the latter relies on the system and structure.
6. Processing and Verification: Several Things That Must Be Decided in Advance
Drying. Nylon elastomers contain amide segments, so moisture absorption must be addressed. If the material becomes damp in packaging, it will directly affect foaming and performance. The drying window is determined based on the actual measured moisture content.
Matching of foaming process. Supercritical foaming requires the melt strength of the material. The same material may perform completely differently under different foaming processes, so the process and the material must be developed together and cannot be selected separately.
Molds and shrinkage. The midsole is a thick-walled special-shaped part, with uneven shrinkage. Mold compensation must be done per piece.
Storage and transportation. The midsole is a semi-finished product, with portions stored both in the factory and in the retail store.
High humidity will accelerate hydrolysis, and strong light will cause light-colored parts to yellow prematurely.
Packaging and storage conditions should be included in the operating requirements.
Many conclusions of 'the materials are no good' actually, when traced back, are problems with the warehouse.
Fitting and post-processing. The midsole should fit with the outsole and upper, and the adhesive and treatment agent should be selected together.
Material surface exudation can cause bonding failure, and this should be considered together with the additive system.
Shoes that don't stick properly cost more to repair than to replace the materials.
Foaming also has another often overlooked variable: the mold temperature distribution.
If the mold temperature is uneven, the bubbles will be larger on one side and smaller on the other, making the feel different on each side of the same shoe.
First measure the mold temperature distribution, then adjust the foaming parameters.
This step is often skipped in shoe factories, yet it is a cost-effective improvement.
The consistency of the bubbles relies half on the material and half on the mold temperature.
Verification order. It is recommended to arrange it like this, do not change the order:
1. Material Level: Resilience, permanent deformation under compression, density, low-temperature resilience
2. Sample Level: Comparison of samples under different foaming conditions
3. Finished Product Level: Density distribution and geometric dimensions of the whole midsole
4. Fatigue level: Simulate compression cycles, remeasure rebound midway
5. Environmental Overlap: Low Temperature Humid Heat Ultraviolet
The order cannot be changed. If the previous level is not passed, just move on, the data that comes after has no explanatory meaning.
7. Boundaries: When This Matter Should Not Be Discussed
For the following four situations, it is not recommended to proceed with this part using nylon elastomer:
First, purely mass-market models, with very tightly controlled unit prices. The cost of nylon elastomer is several times that of EVA. When used in midsoles, it only pays off if the positioning is high enough.
Secondly, production lines without matching foaming process capabilities. Nylon elastomers cannot be used just by changing the material; the melt strength and foaming window must be matched. Without process support, even good materials cannot produce good midsoles.
Third, the usage environment has been long below the material's low-temperature applicable range. At that temperature, the elastomer's rebound and toughness are insufficient, and other systems need to be considered.
Fourth, the usage is so small that it can't cover the development costs of the process. The material verification for the midsole was done together with 'material and process', which required a significant investment.
Fifth, only make shoes for single-use or short-term use. These types of shoes do not last long enough to reach the stage where their rebound retention advantage is evident.
Using a high-cost system is a waste; EVA is more suitable.
Sixth, the production line does not have drying and humidity control conditions. Nylon elastomers are sensitive to moisture absorption.
Without drying and workshop humidity control, batch stability cannot be achieved, so conditions should be improved before discussing material changes.
Writing these six points first is not to discourage, but to save time.
8. Separate accounting for two sets of books: a reconciliation table
Instead of classifying by material, changing to 'watch what when' makes it even clearer.
| What are you looking at? | When to watch | How to measure | Who cares the most |
|---|
| Instant rebound | Material selection, sample making, extracting selling points | Resilience Test | Products and Market |
| Rebound retention | Fixed service period, fixed whether to change materials | Compression Set Fatigue | Quality and After-Sales |
| Low-temperature rebound | Set sales region and season | Low-temperature rebound test | Products and Regions |
| Pore uniformity | Set process window | Section Microscopic Observation | Manufacturing and Technology |
The thing that should be taken from this table the most is not the names of the indicators, but the 'when to look' column.
During the material selection stage, only the instantaneous rebound is considered, which is equivalent to leaving the after-sales problems to the after-sales service.
Items that should be tested during the material selection stage should not be delayed until after shipment.
There is also one more sentence: The priority of these four items changes according to the positioning.
The standard version prioritizes cost control, while the racing version prioritizes controlling rebound retention.
First determine the position, then set the priority; the order cannot be reversed.
Material Change Risk List (From EVA to Nylon Elastomer Midsole, things that need to be changed)
| link; segment; part | What needs to be moved? | Points that are easy to overlook |
|---|
| Mold | The shrinkage and cooling behavior is different, basically requiring a restart or major changes. | Use the shrinkage rate of the EVA mold |
| Dry | Nylon elastomer needs to be dried, and the window should be set according to the moisture content. | Continue the habit of not baking EVA |
| Craft | The foaming window needs to be rematched with the melt strength | Follow EVA's foaming parameters |
| Material Temperature / Mold Temperature | The processing window is narrower than EVA, it needs to be redefined. | Give only according to the supplier's recommended value |
| Demolding and post-processing | The cooling and shaping methods may be different | Follow the original cooling time |
| Color difference | The system is different, the color palette needs to be reconfirmed | The yellowing standard for light-colored parts should be set separately |
| Verification order | Materials → Samples → Finished Products → Fatigue → Environment | Only perform static testing |
One-page report sheet (for people who need to report upwards)
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Project: Shoe Midsole · Material Route Evaluation
Conclusion direction: Nylon elastomers (TPAE / PEBA) can serve as a candidate route for mid-to-high-end positioning
1. Three Rules That Must Be Followed
1. The rebound rate and the permanent compression deformation should be measured together, with the latter carrying more weight.
2. Low-temperature rebound is assessed according to the actual usage temperature
3. The materials and foaming process must be developed together
2. Precondition (It is recommended to postpone if any are not met)
· Product positioning can support material costs
· Has matched foaming process capability
· The minimum operating environment temperature is within the system range
· Cyclic budget for fatigue and aging verification
3. Next Steps
1. Take the existing midsole and measure the compression permanent deformation decay curve
2. Compare rebound based on the actual minimum temperature
3. Small batch trial foaming to check density and pore uniformity
Risk Warning: The main uncertainty of this route lies in the long-term rebound maintaining consistency with the process, not in the initial rebound rate.
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Two questions readers often ask
Question: Are TPAE and PEBA the same thing?
They all belong to the category of nylon elastomers and all have a polyether block amide structure, but the combination of hard and soft segments is different, resulting in different performance tendencies: some are more elastic, some are better at low temperatures, and some are more heat-resistant. You can't just generally talk about 'nylon elastomers'; you need to refer to the specific model's hard and soft segment structure when asking.
Question: Is it better for the midsole to have a lower density?
Lightweight is the goal, but lower is not always better. If the density is too low, permanent deformation under compression and rebound retention will worsen, and it will collapse after short use. Essentially, there is a trade-off between being lightweight, having good rebound, and being durable.
Conclusion
The selection of midsole materials for shoes, ultimately, is a matter of long-term durability, not of immediate tactile feel.
There are only three judgment chains:
Determine the cost ceiling → Set rebound retention for the service life → Define temperature limits based on the usage environment.
Once all three are decided, the question of 'what material to use' naturally has an answer.
If you currently have a midsole project and need to decide on materials, just send over three things to get guidance: target positioning, expected service mileage or months, and minimum operating temperature.
Add a sentence: As for the midsole, most of the money spent on verification is basically on 'time'.
Both compression fatigue and aging need to run cycles, schedule first, then discuss the price.
Standing between the resin factory and the injection molding factory, the matter of midsoles actually already has half of the answer written—it’s written on the consumer's odometer, not on the material property sheet.
What we do is very specific: we take resins like PA6, PA66, PA46, PA11, PA12, PA6T, PA9T, and nylon alloys, and turn them into a form that can actually be used for a certain part; we also do modified PPO, PPS, and thermoplastic elastomers along the way.
Also operates the nylon resin, secondary-grade materials, and bulk materials of major chemical giants, and has long-term purchasing of nylon raw materials, sprue back materials, and various types of nylon waste, with proper disposal channels.
The material selection and mold trial for this type of part can be discussed together.
