At room temperatures, silicones and TPEs can have very similar properties. They’re also similar in appearance. At elevated temperatures, however, silicones exhibit better resistance to chemicals and abrasion. Heat and chemicals aren’t usually associated with infant care products, but consumers boil baby bottles, pacifiers , and sippy tops – or treat them with steam or chemical sterilization. Baby spoons, plates, and cups that are put in the dishwater are subjected to abrasive detergents and hot water.
When subjected to heat or repetitive usage (such as squeezing), TPEs can deform permanently. In other words, products made of these materials may not return to their original shape when heat is removed or usage stops. By contrast, silicones have superior memory and elasticity at a wide range of temperatures – including heat. Plus, silicones maintain their material properties over a virtually unlimited amount of repetitive usage.
Silicones and TPEs also differ in terms of available durometers, or hardness. Lower-durometer elastomers are softer and more compressible. Higher-durometer elastomers are harder and more impact resistant. Silicones have a typical range of 3 to 80 durometer on the Shore A scale. TPEs have a typical range of 20 to 95 (Shore A). As durometer relates to performance, silicones also have a lower-durometer “sweet spot” (50) than TPEs (70). For optimum sealing, however, 30-durometer silicone is a good choice.
For designers of infant care products, choosing an elastomer with the right durometer is critical. Teething rings that are too hard can hurt an infant’s mouth, but a grip toy that’s too soft won’t help a baby to build dexterity. For products that require a super-soft elastomer, gel-like silicones on the Shore 00 Hardness Scale have low levels of surface bleed, the release of oil from the surface of cured rubber. Super-soft TPEs are available, too, but these materials have higher levels of surface bleed.