I wear it on days down to the low 50s. It is quite thin and I have no trouble fitting it beneath my helmet. Note that it is a headband, not a cap. It keeps my ears and for head warm, exactly as I had hoped. It does make wearing glasses a bit more challenging, as my ears are no longer available to secure the temples. Sticking the temples under the headband and over my ears defeats the purpose. It also is very noisy. Wearing the temples over the headband makes them feel less secure and may not work for trail riding. I use this only for road riding.