This is my 4th Garmont boot. The lasts that Garmont uses fit my feet better than any other brand out there. I have a narrow boney foot and have always used race plug boots to get a good fit - with the resulting problem of a very stiff boot. When I started to ski more off piste, I discovered Garmont. I wear a size 10 1/2 shoe. In the Adrenalin I skied a 26.5 - the boot was never long enough and I moved into a 27 - this needed some fitting to get the boot snug enough though. The Radium size 27 fit like a glove right out of the box - perfect length (toes wiggle and stay warm) and snug and the fit remains excellent after 1 full season on them. Awesome boot though a bit soft for stiff skis in-bounds. This boot is a definite improvement in design over the Adrenalin. I also purchased the Endorphin. The size 27 was too snug in the toes. The 27.5 Endorphine fits as well as the Radium and is stiffer (but not Dynafit compatible). If you plan to spend a significant amount of time inbounds, I'd recommend looking at a stiffer Garmont model than the Radium (e.g. the Axon). Finally, I have a pair of Garmont SynerG telemark boots - soft, used to drive a pair of Karhu Guides around logging roads mostly. Size 27 gives me the same perfect fit. So, if you have a thin foot and are looking for a performance fit for AT, Garmont is definitely your boot.