Nalgene™ polymethylpentene flasks offer the accuracy of standard glass flasks combined with the break resistance of plastic. Individually calibrated gravimetrically TC/TD at 20°C. Graduated- printing is durable and won't wear off. Guaranteed to meet the Class B accuracy requirements of ASTM E288 and ISO Standard 384. No meniscus to confuse readings. Translucent and leakproof. Can be autoclaved, but accuracy will be affected. Before autoclaving, set closure on top of the container without engaging the threads.