These flasks have the toughness and transparency of polycarbonate with the utility of polypropylene screw closures. Use for preparation and storage of culture media and many culturing techniques. Safer than glass flasks for use in shakers. The closures are linerless and non-contaminating. The flasks are autoclavable, but these polycarbonate ones show some loss of mechanical strength after repeated autoclaving. The mouth can be flamed gently if desired.