100% silicone have a specially designed cap that makes it easy to pull the valve in and out, keeping the suction constant. provide strong suction that allows for the possibility of producing sufficient milk. adapt to all dr browns™ breast pumps it is recommended to replace the valves every 3-6 months. dishwasher safe and sterilized safely. it is recommended to use a basket for small items when placing in the washing machine. bisphenol-a free packaging: the package includes two (2) replacement valves