Spun glass fiber is used for impingement filtration, with fibers having an adhesive application for improved particle retention. The fibers have a curly tendency which improves resiliency to air flow. Fiber size is usually 8 - 10 denier, or 25 - 30 microns. Density of the media is dependent upon application. Thickness of spun glass pads varies from 3/8 inches for room air conditioning applications to five inches for some transportation uses. The two inch thick filter is used in most commercial/industrial applications, while one inch is standard for most residential furnace filters. Pads or filters are discarded after use. Some health concerns have been raised over the likelihood that fibers might break off during filtration, enter into the circulating air and become respirable. Some experts maintain that continuous filament glass fiber lessens that likelihood. While synthetic media has been used as an alternative to glass fiber, the glass market erosion has leveled off; even with synthetic media capturing a portion of the glass fiber market, growth has been steady at nearly four percent per year, with cleanrooms and new building construction as areas of continuing expansion.

As with glass mat, micro glass is a spun glass fiber, but manufactured at a micron denier size for finer filtration applications, such as battery separator materials, and filter media for ULPA and HEPA filters.