Corning 50mL clear polypropylene (PP) self-standing centrifuge tubes come with the advanced polyethylene CentriStar caps and are bulk packed 25 per resealable zip lock bag. The CentriStar cap has an easy-on/easy-off flat top and offers advanced ergonomics with its wider knurls and roll-over edge design for easier gripping. This leak-proof design comes with a revolutionary plug feature that virtually eliminated all seepage when used under recommended conditions.