The Federal Housing Administration (FHA) sets regulations about carpeting weight and density minimums legally required of carpet manufacturers. These regulations are broken down into two types: Type "1" is for single or multiple family dwellings and Type "2" is for elderly housing or care-type housing. Regulations are further broken down into two classes: Class "1" for both types pertains to moderate foot traffic, whereas Class "2" represents heavy traffic or use areas.
Type 1 (Single and multi-family), Class 1 (low traffic use) polyester carpet must have a minimum weight of 32 oz. per square inch. This is face weight, not total weight. The difference between the two is face weight is a measurement of the carpet, alone; total weight is the measurement of the carpet and all backing material applied to it. Carpets to be used in these single/multi-family housing types that expect heavy carpet traffic (known as Type 1, Class 2) are required to have a minimum face weight of 40 oz. per square yard.
Type 2 dwellings, which consist of nursing homes and other elderly or care-type homes, are required to have a minimum of 32 ounces of face weight for low traffic use (Class 1). A minimum weight isn't applicable for Type 2, Class 2 polyester carpeting, as it isn't produced for this clientele served.
The FHA requires that the fibers of polyester carpeting meet minimum density requirements as well. Density--the degree to how close each fiber strand is to another at the base of the carpet, as well as how many strands of fibers the carpet contains altogether--varies based upon polyester carpet type and class too. Type 1, Class 1 polyester carpet minimum FHA requirement for density is 1,500. Class 2 minimum in this type is 1,920, to ensure heavier traffic doesn't mat down the product easily.
The higher the density number the less matting and the less evidence of foot traffic patterns across the carpeting. Higher density carpeting is often used near doorways and areas that will experience more use. In Type 2 settings, such as nursing homes, the minimum exists only in regards to Class 1 products, which requires a minimum of 1,550 density.
Higher ounce weights do not ensure a polyester carpet that will not mat or provide a plush covering beneath your feet. Higher "face weights", however, coupled with densities in the neighborhood of 4,000 will be more likely to do so with this particular carpeting type.