This innerwear boasts excellent heat retention, incorporating NASA technology. It's a great deal at less than half price. Size is L. I cut the tag off intending to use it, but it's only been tried on. Material: 96% Polyester (46% hollow fiber) / 4% Polyurethane Product Details: ・Microthermal capsules store heat released from the human body and, upon reaching a certain temperature, dissolve and release heat. ・The heat retention effect of the microthermal capsules is incorporated into the fibers and is repeatedly effective. ・NASA's microthermal capsule technology is used in this inner jersey.