Complies with ISO 4797 and ISO 1773, Manufactured from 3.3 expansion borosilicate glass complying with ISO 3585 (ASTM E-438 Type 1 Class A), The flat base allows use with hotplates, FF150/3S, FF150/4S, FF150/5S and FF500/2S are supplementary to ISO 4797., Note: These flasks are not suitable for use under a positive or negative pressure