Although not a terribly common behavior, some cats will chew or suck on different types of fabrics and materials. This behavior is referred to as ‘pica’. It is not well known why cats do this, but some theories are that the cat is suckling similar to what it did as a kitten (when feeding from the mother cat’s nipple). It is thought that this suckling might have a calming, relaxing or pacifying effect.
Cats who don’t grow out of suckling as a kitten may continue it into adulthood. At which point they may not only suck on, but also will chew and may even eat different fabrics. Common fabrics are wool, cotton and other synthetic materials (even plastic garbage bags). This behavior seems to be common to Siamese and Burmese cats and cats who are weaned very early (before 4 weeks of age). Some cats who do exhibit this behavior may swallow fabric and this can cause a host of digestive problems in the cat.
The best way to limit or stop this behavior seems to be keeping the cat calm and happy. You may want to start off by hiding the favorite fabric. For instance if your cat chews wool, keep your sweaters and other wool products in closets that can’t be opened by your cat etc. Next make sure your cat is calm and has no reason to be upset. Many cats will start this behavior when they are stressed or ill, so make sure there is no reason why your cat would need to do this behavior to relax (some behaviorists put cats with this behavior on anti-depressants to keep them calm and happy). Do NOT punish or yell at the cat for this behavior; this will only increase the cat’s stress and compound the problem. You might also want to purchase some toys for your cat that he can chew, that way if he needs to chew he will have something acceptable and distinct from what he used to like to chew. And lastly make sure your cat isn’t simply hungry. Many times cats do this to try to feel like they have a full belly because they are simply hungry.