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Covering Material-polypropylene
QUESTION:
What is the covering material used on D.E. filter grids and is this a special fabric?
  ANSWER:
The cloth used on Unicel's D.E. grids is 100% Polypropylene. This fiber, a member of the Polyolefin family, has excellent resistance to acids, alkalis, and abrasion, in addition to being both rot and mildew resistant. The use of polypropylene cloth for swimming pool filtration was originally developed by Meissner Mfg. Co. (Unicel's parent company) during the 1950s. Throughout the forty-year span that polypropylene cloth has been used in this application, this fabric has gone through several modifications. Improvements to critical properties such as yarn construction, weave pattern, and fabric finishing have allowed us to better control the fabric's "permeability" in order to optimize the D.E. cake handling characteristics. Permeability is the cloth's flow resistance, expressed in "cubic feet per minute" of airflow as measured with a Frazier permeability machine.

If D.E. grid cloth has too low a permeability, it will blind off quickly, resulting in short filter runs and frequent backwashing. On the other hand, if the material has too high permeability, D.E. can bleed back into the pool. For this reason, all polypropylene grid cloth used by Unicel (and Meissner Mfg.) is woven and finished to our exacting permeability specifications. As a result, we can assure the user the optimum in filtration efficiency, dirt holding, and cake release properties without D.E. kick back or short filter runs.