Corning® 15mL clear polypropylene (PP) centrifuge tubes come with the advanced polyethylene CentriStar™ caps and are bulk packed 50 per resealable zip lock bag. Foam racks can be purchased separately. The CentriStar™ Cap has a 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 eliminates all seepage when used under recommended conditions.