Multi-density PU engineered for the hours the product is actually worn.
- PU resists compression set; EVA is lighter and cheaper but flattens sooner — the split is hours worn, not price
- Roughly 40% better abrasion resistance on ASTM D4060, and support holding 6–9 months against EVA's 3–6
- Plantar pressure is not uniform: heel strike highest, metatarsals high at push-off, medial arch low but needing support
- Zoned density lets each area be tuned to its own mechanical job instead of compromising across all three
- Hardness is not support. Support is geometry; hardness only sets how far the foot sinks
- Figures here come from material literature — publish only what your finished product has been tested for
1. PU versus EVA: the split is hours worn, not price
EVA wins the first day and PU wins the sixth month. On a shop floor an EVA insole feels light and soft; six months of standing later it has taken a compression set and the thickness that used to carry the load is gone. PU holds its original thickness far longer, which is why occupational footwear that has to keep performing tends to be specified in PU despite the higher unit cost.
2. Plantar pressure decides where the densities go
The sole of the foot does not load evenly, so an insole should not be uniform either. At heel strike the rear of the foot takes the largest single impact; at push-off the metatarsal heads take the peak; the medial arch sits at low pressure throughout and yet is the area that collapses if it is not held. Those three facts, taken together, are the whole argument for zoning.
3. How a multi-density insole is laid out
Read as a longitudinal section from forefoot to heel, a functional PU insole is three mechanical jobs stacked into one part.
| Zone | Mechanical task | Density choice |
|---|---|---|
| Forefoot | Absorb the push-off peak at the metatarsal heads | Lower density, cushioning first |
| Medial arch | Hold the arch without collapsing | Medium hardness, stiffness first |
| Heel | Absorb strike impact and stabilise | High density plus a 3D cup |
| Top cloth | Manage moisture and surface feel | Moulded in one shot or laminated |
| Base layer | Stop the insole sliding inside the shoe | EVA anti-slip base |
4. Where PU needs formulation work
Two behaviours of polyurethane are worth naming rather than glossing over. Hydrolysis over a long service life in humid conditions, and yellowing with UV exposure. Neither is a reason to avoid PU; both are handled at formulation level and by setting a sensible storage recommendation. Tell us at requirement stage if the product will sit in stock a long time or ship to a humid market.
5. Construction options
| Option | What it gives | Trade-off |
|---|---|---|
| Single density | Lowest cost, simplest process | No zoned feedback |
| Dual / multi density | Each zone tuned to its own task | More tooling, more process steps |
| One-shot fabric moulding | Material-level bond, resists delamination | Changing the cloth means re-sampling |
| Post-laminated facing | One body, several colourways | Adhesive quality becomes a QC focus |
| Graphene fused into the body | Heat spreading and abrasion reinforcement | Dispersion control at compounding |
The full construction discussion, including facing routes, is on Insole OEM / ODM.
6. Frequently asked
It depends on how long the product is worn at a time. EVA feels better on day one and is lighter and cheaper; PU holds its thickness far longer and resists abrasion roughly 40% better on ASTM D4060. For a standing occupation, where an insole that has flattened is an insole that has stopped working, PU is normally the right answer. For a promotional or price-led line, EVA is.
Under regular use, support typically holds for around 6–9 months against 3–6 months for EVA. Both figures move a great deal with body weight, hours worn per day and the environment, so they are planning numbers rather than a guarantee. Replacement interval is worth stating in your product literature.
The plantar surface does not load evenly. The heel takes the highest pressure at strike, the metatarsal heads take the peak at push-off, and the medial arch is a low-pressure area that nonetheless has to be held up. One hardness across the whole insole has to compromise on all three; zoning lets each area be tuned to the job it actually does.
No, and this is the most common specification error. Support comes from structural geometry — arch elevation and heel cup depth — while hardness only governs how far the foot sinks. Making the whole insole harder fatigues the sole faster without ever holding the arch up.
Yes. PU is a good host substrate: graphene can be fused into the body for heat spreading and abrasion reinforcement, and latex or memory foam layers can be laminated for a different surface feel. See Graphene Functional Product OEM and TakeSoft Patented Latex OEM.
Both are real behaviours of polyurethane over a long service life and both are addressed at formulation level rather than ignored. Where a product will be stored a long time or used in a humid environment, tell us at the requirement stage so the formulation and the storage recommendation can be set accordingly.
The abrasion and service-life numbers here come from material comparison literature, not from a test of your finished product. To publish a figure, have the finished item tested under the corresponding method and state the method. We can supply process and material information to support the submission.
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