Teat section has an ?accordion-like? portion that enables it to stretch in response to the peristaltic movement of the baby?s tongue. Ultra-Soft Silicone. The nipple?s surface is very soft, yet it does not collapse easily. Made from thick ultra-soft silicone material, the nipple has similar elasticity to that of a mother?s actual breast. The dome-like shape makes baby?s mouth open naturally, supports its mouth softly and fits its lips gently.