A great winter cycling cap has to block the oncoming wind and weather, fit well under a helmet, a brim that offers some coverage and offer plenty of warmth, while breathing out excess heat and moisture from perspiration. Castelli rates the Estremo WS Cap from 20-50°F and it certainly favors the coldest temps for most cyclists who enjoy some extreme winter training. Utilizing the superior stretch, wind blocking, and water repellency of Gore Infinium Windstopper X-Fast lightweight, 4-way stretch softshell material, Castelli gets the protection and insulation you require, along with breathability, all without bulk. The fit is a byproduct of the panel design and stretch.

To add extra insulation, especially for the lower ears and neck, a flap of Castelli's own Warmer fleece fabric is employed. The ultra-soft Warmer also breathes well, but lacks the water and wind repellency of the X-Fast. For that reason the Estremo WS Cap is perhaps best suited to cold, dryer, conditions, though light snow or rain won't be a problem. Castelli has taken pains to band the lower edge for greater durability and provide a better finish quality, and we were originally concerned it would create awkward helmet interaction, but were pleased to find it did not. The panel seams are cleanly finished and barely noticeable inside, or when you have your helmet strapped on.

The Estremo WS Cap is perfect for serious cold, dry winter cycling for those who prefer a true cycling cap with a brim versus just a skull cap. That is a personal preference. We can tell you the Estremo WS Cap is seriously warm, so if you always feel you need a bit more warmth, it should be your top choice below 50 degrees.