I had some time on my hands last week & visited an outfitter in New England. Tried some things on.
Patagonia has added to their long-standing R1 light fleece offerings with something called R1 Air. Fluffy-looking fleece. It's nice, but it's cut very slim/athletic. I'm normally fine with their size XL, but on this one, it was too confining. Maybe the intent is to wear it more like a base layer. They didn't have XXL to try on, so not sure if sizing up would work or not. I have had to size up with a few Patagonia layers in the past - an old version of the nano air was really tight on my forearms, so i went with XXL. Sometimes, when they introduce a new line, this happens, or maybe they're thinking people lost weight last year?
Tried on a Smartwool long-sleeve layer, the Intraknit merino 200 crew. It's 53% merino, 45% polyester, 2% elastic. Love the fabric - it's substantial & stretchy, but again, slim fit. I have older Smartwool baselayers, a zip neck i have had for at least a decade, and size XL fits well, meaning it doesn't fit like a glove, has a little room. the Intraknit fits like a surgical glove. The outfitter didn't have XXL to try on.