I bought this cap for running and walks in the forest. The material is thin, so it is suitable for running and very comfy to wear. Perfect for summer outdoor, but for a daily street wear cap I prefer other models with some thicker material.
My head is 57 cm and I took M, however, it runs big on me - pulling it down some for a better fit, it leaves a kind of bump and headroom. To compare, my wife's S size cap fits me perfectly and feels like to most 'all size fits one'.
