Spun fabrics are produced by yarns that are made up of short staple fiber. All natural fabrics such as cotton and wool will always be spun fabrics as we're unable to produce natural fabrics in continuous filament. Synthetic fabrics such as polyester, polypropylene, nylon, corder, etc., can be produced in staple or spun fabric form. Spun fabrics tend to be rated with the best efficiency or retention, will have generally lower flow rates, will be more likely to blind, and have the poorest cake release. They also will generally have the better abrasion resistance.
Spun fabrics like multifilament fabrics may be scoured, heat set, calendered or finished otherwise, to release built-in yarn tensions during the weaving process so that once the fabric is installed in a fabricated form on our filter, it will retain the form we have fabricated. Without heat setting or finishing, this fabric will very likely shrink and may possibly even stretch and take a different shape than originally fabricated.
Spun fabrics are produced from spun yarns and their yarn size generally is classified as a woolen system, a worsted system, or a cotton system. Generally, the fabrics we use in the liquid filtration will be produced by cotton system yarns and will be numbered, such as, a 12/1, a 6/1, etc. The yarn numbering system here is just reverse from the denier system discussed in the filament yarn. For example, a 12/1 yarn is half the size of a 6/1. Spun yarn applied in which case they would be noted as 12/2, for example, the 2 being a 2-ply. We may at times find a 12/3 which it means it would be a 3-ply yarn. Again, spun yarns must be twisted so that the individual staple fibers will be held together creating the yarn bundle. Generally, spun yarns may have 12 to 15 turns per inch depending on the type of yarn and staple length. cotton yarns, for example, may have a fiber length of only 1" to 11/2" long. Polypropylene's spun yarns are synthetic yarns may have staple lengths from 2" to 4" in length.
The weave patterns for spun yarns generally are those as we find in multifilament, such as, plain weaves, oxford weaves, twill weaves, satins, etc.