Tubes are made from borosilicate glass in compliance with ASTM Specification E438, Type I, Class A or B glass requirements. With conical shaped bottoms on the 5, 10, and 15 mL sizes and a bullet nosed shape on the 50 mL size to withstand centrifugation up to 2980 RCF. Tubes are plastic shrink wrapped in modular trays for cleanliness and safety. Closures are not supplied.