These lightweight sweatpants are made with a special three-layer fabric that combines heat retention and breathability. The stretchy knit fabric, made from recycled materials, is formed into a three-layer structure with a cardboard-like air chamber, creating a knit fabric structure that is thick yet light, and prone to generating dead air for excellent heat retention. The elimination of side seam stitching improves comfort. They can be widely used from training sessions to everyday wear. They are designed with electrostatic care to suppress the generation of unpleasant static electricity. No stains, tears, or odors.