VWR® Erlenmeyer Flasks, Narrow Mouth, 500 mL, 10536-926 Flasks are durable and come with reinforced rim for easy pouring and also avoids any breakage while washing. Borosilicate glass fabrication Durable design Feature durable white ceramic enamel scale which indicate approximate volume for measuring and mixing. Manufactured from ASTM E438 Type 1 Class A borosilicate 33 expansion glass. As per ASTM specification E 1404 Type 1.