Acrylic is the "workhorse" hand-crafting fiber for crafters who knit or crochet; acrylic yarn may be perceived as "cheap" because it is typically priced lower than its natural-fiber counterparts, and because it lacks some of their properties, including softness and propensity to felt. The fiber requires heat to "relax" or set the shape of the finished garment, and it isn't as warm when wet as alternatives like wool. Some hand-knitters also complain that the fiber "squeaks" when knitted, or that it is painful to knit with because of a lack of "give" or stretch in the yarn. On the other hand, it is machine-washable and extremely color-fast. This makes it useful in certain items, like garments for babies, which require constant washing. However it is much more flammable than its natural fiber counterparts, so caution should be used when making items for babies and children.