I’ve had this helmet cover for a few years, and since I busted it out today to use it, I thought I’d put up a few pics. It’s pretty simple: a goretex cover with an elasticized edge, that fits on your helmet like a big shower cap.
I tend to wear Lazer helmets in L/XL. The Gore helmet cover I have is a Large; it fits perfectly. It has a little bit of room to go to a larger helmet, if need be.
Today, it was low 50s, windy and raining. Perfect conditions for the helmet cover. With a lightweight cycling cap under my helmet to help manage sweat, the cover did a perfect job of keeping my head dry, in everything from downpour dumping rainstorm to light mist. It is totally windproof, and surprisingly breathable. Wearing it with a cycling cap is a great idea–the cycling cap helps manage moisture from your head, and the air gap created by the helmet gives the goretex membrane a good opportunity to be breathable and let that moisture out, without letting rain in.
When the temp drops, it’s easy enough to wear a warmer hat underneath the cover, and stay warm. By itself, it isn’t terribly warm (though it is waterproof and totally windproof). It maybe adds an extra 5 degrees of comfort to whatever you’re wearing, if it isn’t raining. It’s a great piece of gear for inclement weather. Note that because it covers the whole helmet and doesn’t have holes, it will not work with most helmet mounted headlights. Unless you’re using an alpine headlamp, this likely won’t work. That’s the price of being rainproof.