High purity glass microfiber thimbles manufactured from 100% pure borosilicate glass are available for specialized applications. The thimbles are completely free of binders or additives and can be used at temperatures up to 500° C or when using solvents incompatible with cellulose thimbles. These thimbles are also used in pollution monitoring techniques (0.8 µm nominal particle retention). Typical thickness 1.7 mm. Applications include: smoke stack gas monitoring, Soxhlet extraction, analyzing pesticide residues, determining oil/fat content of foods, analysis of oil and grease in solid wastes.