These popular caps fit plain end culture tubes and flasks with DeLong style necks or ports. The caps are molded from durable, autoclavable polypropylene (PP). They are available in a full range of five sizes and five colors for easy sample identification and organization. Recommended tube diameter is indicated on each cap. Reduce sample evaporation compared to cotton plugging. Provide same evaporation and sterility benefits as stainless steel closures.