Polypropylene clothing should be washed in cold or warm water and hang to dry, or VERY LOW dryer heat. Polypropylene, being a plastic polymer, has a low melting point and care should be taken to keep the material away from high heat or open flames. To maintain your clothing’s hydrophobic properties, do not use fabric softeners or dryer sheets on polypropylene fabrics or put in the dryer with heat. For best results, wash in cold, or warm water and hang to dry. Polypropylene is designed to be the best extreme cold base layer of clothing worn next to your skin. No other fabric is more suited for the job. Polypropylene is not the most stable fabric worn on the outside. In the presence of UV rays polypropylene may fade over time. Polyester is a more stable fabric for outer layers and its ability to repel water. A layered combination of Military Thermals Polypropylene and a Polyester shell is your best combination for extreme cold weather comfort.