Common materials include medical‑grade silicone (often used for collectors), plastics such as polyethylene or polypropylene (used for bottles and pouches), and occasional stainless steel used in some insulated coolers.
Closures vary by product: pouches commonly use threaded twist‑lock caps, bottles typically have screw‑on lids, and silicone collectors rely on internal supports and a stable base to reduce spills while worn or resting.
Some systems provide direct pump‑to‑storage transfer using twist‑lock fittings or specific pump adapters so you can express directly into a pouch or bottle; product listings will note explicit breast pump compatibility.