Size: L Already have the Terrex cap and wanted a second one as like the Koumori range. Size fits the same as the Terrex one (I didnt measure my head just went for large) - There is a lot of adjustment available which is very useful for different head sizes and shapes. Very comfortable, machine washable and dries very quickly which is good for me as a bit of a head sweater. Unlike the Terrex cap there isn't the plastic form in the peak but it still keeps its shape well after numerous washes (quite often hand wash and wring out in post run shower). On initial wear it does feel like the cap fits high on the head and might 'pop-off' but this is not the case and you do get a secure fit on your head. Not sure on the clip on the back, but you can of course remove it but mine is still on it after numerous uses and dont intend to remove it now. Definitely a good investment as I have destroyed a lot of 'fashion' caps by wearing them for runs etc