Designed for use on any reusable bottle system. Stage 1, 0-6 months. Playtex Premiere Stage 1 nipple provides a slower flow designed especially for younger babies. Special air vents allow liquid to flow smoothly on demand without the frustration of collapse or leakage. Clear, medical grade silicone is soft on baby's gums and fits comfortably in baby's mouth. Designed for use on any reusable bottle system.