I needed this product for cold winter riding and was unhappy with the fit of other skull caps. This one has proved servicable to below 40 deg and has a nice tight seal around the edge. Only thing I would ask for is a size between S and L and $10 less expensive.
This helmet cap does an amazing job at keeping my head and ears warm on rides down to the 30s. From the size chart I fell between a regular and large so went with larger size. Wish I had stayed with the smaller version because the larger size is a bit loose. There is very little stretch in the fabric so getting the right fit may be difficult.
I have been out with the Windstopper Helmet Cap with wind chills in the mid 20s. Michigan winter came early! This cap does the trick. I use to have to put Cotten in each ear to stop earaches. Not anymore. Now I can hear traffic around me without a massive ear infection. Thanks so much to Gore.