Answer: PTT fiber is called shape memory fiber because when the fiber is once formed, it can remember the initial shape and characteristics given by the outside world. The shaped fiber can deform arbitrarily and maintain it at a lower temperature. The deformation is fixed under temperature (secondary forming) or the deformation is fixed under the forcing of external force. But when deformed fibers encounter specific external stimuli, the fibers can return to their original shape. Currently, there are two representative PTT fibers in the world: Shell Company of the United States and DuPont Company of the United States, whose production has an absolute monopoly. The main characteristics of PTT fiber: it has the stability of polyester and the softness of nylon. Its performance is as follows: 1. PTT fabric is soft and has excellent drape. 2. PTT fabric has comfortable elasticity (better than polyester PET, polybutylene terephthalate PBT and polypropylene PP fiber, and equivalent to nylon 6 or nylon 66 fiber). 3. PTT fabric has excellent elongation recovery (it can still restore its original length after being stretched by 20%). 4. PTT has excellent dyeing and printing properties (general disperse dyes can be dyed at 98℃-110℃); excellent dyeing fastness, light fastness and stain resistance. 5. PTT fabric has bright colors and is easy to iron. 6. PTT has a wide range of adaptability. PTT is suitable for pure spinning or compounding with cellulose fibers, natural fibers, and synthetic fibers to produce carpets, casual clothes, fashionable clothes, underwear, sportswear, swimwear and socks.