Filters with a minimum efficiency of 99.97% for 0.3Ám particle size as determined by test. The test can be by the monodispersed dioctyl phthalate (DOP) method or other equally sensitive method. When operated at design velocity, larger and smaller particles are captured at higher efficiencies. HEPA filters are made of compressed and bonded micro-fiberglass or Teflon« corrugated to produce a high surface area in a small area panel of filter medium. Employed in unidirectional airflow benches, air handlers, and as terminal air supply filters in cleanrooms.