This cap is excellent as a lightweight layer. It's warm enough to cover you in spring and fall, but as Anders said, it's probably not for the deep cold. It's acceptable at reducing the wind, but it doesn't stop it entirely. I'd say anything colder than 20 degrees F and you'd be uncomfortable, so bring another layer to top this one. This is very thin, so is exceptionally light and small in footprint folding to just under the size of an iPhone. The weight is negligible as well. Because it is so thin it bears an uncanny resemblance to a swim cap, so it may not be for those looking to make a fashion statement.

It turned out to fit a little smaller than I thought it would, but then again I kinda have a big head. I really enjoy its tiny footprint and it has kept my head warm each time I have used it, down to 30F degrees so far.

As Anders said this cap is excellent for when the wind is down and you just need something covering your head. I've used it for bike riding in NYC from 10 degrees F to 40 degrees F to good effect. The footprint is impossibly small, small enough to be about iPhone size (easy to fit in jeans pocket) This makes it a sure bet for a day hiker who needs something small, exceptionally light weight, and decent protection in a pinch. It also makes a great layer 1 for snow shoeing with a second heavier cap on top. If you're looking for small and efficient this is it.

I love this one, so light and thin, its perfect for when a woolen cap is too much, but you need something on your head. very good against wind and water, while breathing wery well. I have used this in sleet and hail both in the inland and on the coast of northern norway( 66 degrees north), and in clear cold weather in the mountains of southern norway at around 2000 meters, and its great both places. bring a woolen cap to put over in severe cold.

This cap fit really weird. The S/M was adequate in circumference but too short to cover my ears; annoying to wear because I kept wanting to pull it down over my ears. I was disappointed that I had to return it.

It was very small / short. I ordered a small and it didn't cover my ears at all (I have a pretty small head - generally an xs in helmet sizing). I'm not sure if a larger size would have been better - i returned it for something else. The fabric was nice though - typical OR fabric.