Made from polycarbonate.Locking tabs are located in the bottom of each well to allow the user to remove cryogenic sample vial cap with one hand.Raised feet in the bottom corner allow the rack to sit above the working surface.Top left corner is squared for easy orientation.Ribbed gripes make handling with gloves, easier.Drainage holes in each well aid in cleaning.Alphanumeric indexes are embossed with numbers 1-10 running horizontally and letters A-E vertically for quick location and retrieval of tubes