A composite protective yarn is incorporated into an article of apparel. The protective yarn has a core unit including a protective material selected from a group consisting of metallic filament, glass, and high tenacity fiber having a tensile strength of at least 7 grams per denier. A cover is applied to the core unit and is adapted for residing adjacent the skin. The cover includes an optically responsive material adapted for absorbing infrared radiation emitted from the human body at a first wavelength and returning the absorbed radiation to the body at a second longer wavelength. This relaxes capillaries and promotes increased blood flow to body parts covered by the article of apparel.