Engineering Answers / Material & Selection
The three materials can be made to look identical on a shelf. They fail differently in a dishwasher, a hot car and a baby's mouth — which is where the decision should be made.
Silicone is a thermoset that stays flexible from well below freezing to well above boiling, carries the strongest food-contact and skin-contact claims, and does not stain as readily. TPE and TPU are thermoplastics: cheaper, faster to mould, easier to overmold onto rigid parts, but they soften above roughly 120 °C and stain more readily. For kitchen, feeding and skin-contact products silicone is usually the correct default; for grips, cases and hard-soft combinations TPE or TPU often win on cost.
Silicone is a thermoset. Once cured, its polymer network is crosslinked and cannot be melted again. TPE and TPU are thermoplastics: they soften when heated and harden when cooled, which is why they can be injection moulded in seconds and reground.
Everything else follows from that single fact:
| Criterion | Platinum-cure silicone | TPE | TPU |
|---|---|---|---|
| Heat resistance | Holds properties well beyond boiling; autoclavable grades exist | Softens above roughly 120 °C | Softens above roughly 120 °C; better low-hardness retention |
| Low-temperature flexibility | Excellent; stays flexible below freezing | Good | Good, but stiffens faster |
| Food contact | Strongest claim set — FDA 21 CFR 177.2600, LFGB | Food-contact grades, narrower claims | Food grades for repeated-use parts |
| Stain resistance | High; no plasticiser to absorb pigment | Lower | Moderate |
| Feel | Dry, silky, low-friction | Rubbery, slightly tacky | Grippy, abrasion-resistant |
| Hardness range we hold | Shore 20A–80A, ten grades | Broad; soft grades hard to stabilise | Broad; good retention at high hardness |
| Process | Compression or LSR injection; cured in tool | Thermoplastic injection, very fast cycles | Thermoplastic injection, fast cycles |
| Scrap | Cannot be remelted | Regrindable | Regrindable |
| Overmoulding onto rigid parts | With matched substrate and primer | Easy; the standard route | Easy; strong bond to PC and ABS |
| Typical failure | Tearing at a thin wall, compression set in hot service | Softening, staining, creep under load | Hydrolysis in hot humid service (polyester grades) |
Three use cases are not really negotiable.
Food and feeding. A silicone spatula, bottle nipple or suction plate sees hot food, repeated washing and often a dishwasher. Silicone holds its properties, carries the compliance claim and does not absorb colour. This is also why the material is specified as platinum-cure: it crosslinks without peroxide by-products, so it is odour-free and meets food-contact standards without relying on a post-treatment.
Skin contact over long periods. Watch straps, ear cushions, medical wearables. Silicone is soft, non-tacky and does not contain plasticiser that can leach into skin. It also tolerates sweat and repeated cleaning.
Anything that must stay soft when hot. A pot holder, an oven mitt, a sealing ring on a pressure cooker. A thermoplastic at that temperature is not soft — it is deforming.
Hard-soft combinations. A toothbrush handle, a power tool grip, a phone case with a rigid frame. Overmoulding TPE onto polypropylene in one cycle removes an assembly step and a supplier, and the bond is mechanical and reliable.
Cost-sensitive dry goods. A cable tidy, a protective cap, a non-food sleeve. If the part never sees heat or food, paying for silicone's thermal and compliance advantages is paying for properties the product will not use.
Abrasion resistance. TPU is genuinely better than silicone where the surface is rubbed — soles, wheels, tool holsters. Silicone is soft and tears at a thin edge; TPU resists abrasion and can be formulated to a hard, slick surface.
Before tooling is cut, these questions usually decide the material without a long study:
If the answers point to silicone, the next decision is process route — LSR injection for thin walls and tight tolerance, compression moulding for thick sections and lower launch volumes.
The typical mistake is choosing TPE for a kitchen product to hit a target landed cost, then discovering in the first container of customer returns that the parts have yellowed and picked up curry colour. The second-most-common mistake is the reverse: specifying silicone for a purely decorative hard shell, and paying three times the material cost for a property the product never uses.
Silicone is the correct default when the product meets heat, food, or long skin contact, and when the part is mostly soft. TPE and TPU are correct when the part is mostly rigid with a soft touch, when the service temperature stays below roughly 120 °C, and when cost and cycle time dominate. The material decision is really a decision about which failure mode you are willing to insure against.
Food-contact grades of TPE exist and are legitimately used, but the claim set is narrower than platinum-cure silicone. Silicone is typically specified against FDA 21 CFR 177.2600 and LFGB, and it holds its properties through repeated dishwasher cycles and high-temperature food contact. A TPE that passes a migration test at one temperature may not hold the same claim across the service life of a kitchen product, which is why we steer kitchen and feeding items back to silicone even when the target price is tight.
Because it is a highly crosslinked thermoset with a low surface energy and no plasticiser to migrate. TPE and TPU are thermoplastic blends, and the soft phase plus any process oil can absorb pigments from tomato, turmeric or coffee. The difference shows up after months of use rather than on the first day, which is exactly the timescale a brand cannot test in a lab before launch.
Per part, TPE and TPU are usually cheaper: material cost is lower, cycles are faster because the part is cooled rather than cured, and scrap can be reground. Silicone's advantage is that it removes risk — fewer warranty claims from heat and staining, a stronger compliance story, and no plasticiser migration. The honest comparison is total cost over the product life, not the moulded piece price.
Yes, plastic overmolding and multi-material moulding are standard routes. The substrate and the silicone have to be chemically matched or mechanically keyed, otherwise the bond fails in the field. That is a tooling and primer decision made at DFM stage, not something that can be fixed by changing the material later.