I love this product, I bought two & may buy more. When winter biking it's important to have breathable & stretchy material. this shirt is a great combination of both. I wear a light merino wool as an under layer & this is a perfect combo. I bought an XL to wear with no or light under layer & XXL to wear when colder weather hits, I'll wear my Surly merino wool. I'm warm down to 10 degrees. 5 Star product.