The filter is provided with polyester needle-felt envelopes, stretched and sealed around rectangular frames, which can be changed through an inspection door at the front of the filter. Very little space is required per m2 of filter area.
過濾器有滌綸針刺氈的信封，伸在矩形框密封，可通過檢查門在前面的過濾器的。很小的空間是每平方米過濾面積要求。