Polypropylene is a unique synthetic that's extremely hydrophobic—it absorbs virtually zero moisture, making it the most efficient fabric at pushing sweat away from your skin. For high-output skiing in bitter cold, like backcountry touring or hiking for fresh tracks, this can be a real advantage since you stay drier faster than with merino or polyester.
The trade-offs are significant, though. Polypropylene holds onto odor quickly, so plan on washing it after every use—it's not the pick for multi-day hut trips. More importantly, it has a low melting point and can literally melt if exposed to high heat, so you'll need to air dry it and keep it away from heaters or hot dryers.
For most resort skiers, merino wool or a wool-synthetic blend offers a better balance of odor control, warmth, and easier care. Polypropylene really shines for extreme cold, high-exertion days where moisture management is your top priority and you're willing to handle the extra maintenance.