Apex Instruments stocks a variety of fiber thimbles for in-stack particulate sampling. The thimbles are seamless, high purity filters, and available in two different fiber types: borosilicate glass and quartz. Borosilicate glass fiber thimbles are acid-washed to reduce the trace metal content to an absolute minimum. The quartz fiber thimbles are strengthened with alumina and are pre-fired at 900⁰C for 2 hours during manufacturing to stabilize the weight prior to use. The gas collection efficiency of the thimbles is 99.95% (0.3 micron DOP). The 25×90 mm thimbles are specially manufactured for stack sampling and tapered for easy loading. Cellulose thimbles are available upon request.