This 1000ml PYREX® narrow mouth Erlenmeyer flask with a heavy duty rim is made from low expansion, Type 1, Class A borosilicate glass that can be heated directly in an open flame. PYREX® Erlenmeyer flasks are made to ASTM E14040 specifications for general laboratory use such as mixing, heating, and cooling. The graduations are approximate and not intended for accurate liquid measurement. The Pyrex® brand is known for consistent high quality and their Erlenmeyer flasks are used in professional laboratories throughout the world. Use a #9 stopper for this glass flask.