Super-Stretchable 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.