These Enfamil Slow-Flow Nipples utilize a reformulated material to make them softer, which allows for easier suction. They may reduce feeding fatigue. These Enfamil nipples are ready-to-use, come individually wrapped and vented to allow air flow while the baby is sucking. They will fit most bottles with standard or classic size bottle openings. These Enfamil nipples are made from surgical grade plastic and do not contain latex.