Corning 3950 PYREX® 8µm Glass Wool Roving (fiber glass) is made from fine glass fibers with diameters controlled to approximately 0.008mm. This makes the glass pliable and easy to use. Manufactured from No. 9989 glass, this fiber glass contains minimal heavy metals and is suitable for use as a filtering medium. It is supplied in the form of roving approximately 2 inches in diameter by 22 ft. long and packaged in 0.23 kg (½ lb.) bags or in a case qty of 5.52 kg (12lbs).