In reply to Moorland-wanderer:
What do you have to compare them with? I once owned a Patagonia Performance Better Sweater which was too tight, but the same size in the R1 Air Hoody is perfect. Both are slim fit. I also own a Rab Nucleus Hoodie in size M which runs more or less the same as the R1 Air Hoody in size S. Fjällräven Keb Fleece Hoodie in S is also pretty much the same as the R1, albeit with slightly longer sleeves.
The R1 Air Hoody is a perfect active midlayer btw. It's warm when you're passive but breathable when you're active. I wouldn't dare wearing it without a shell though, it seems quite prone to pilling and it feels fragile.