The white version of this is 100% cotton (thankfully!), and is exactly what my husband wanted to wear under annoyingly translucent dress shirts (what is it with 100% Egyptian cotton shirts and sheets? Why have they become so thin in recent years?!) instead of the short-sleeved undershirts he had been wearing before. Under annoyingly translucent shirts, short sleeved undershirts show a distinct difference between the bare arm parts and the shoulders, torso and part of the arms where the sleeves are. A long-sleeve white teeshirt like this makes thin white shirts look much much better (pull the sleeves down to remove wrinkles before doing up the cuffs). I think it improves the look of all dress shirts, but white ones in particular look vastly better this way.
At the same time as I ordered this one, I ordered a Hanes Long Sleeve Beefy-T and a Soffe Men's Men'S Long Sleeve Cotton T-Shirt. Both of those are also 100% cotton too. This Hanes Men's 4.5 oz Hanes NANO-T Long Sleeve T-Shirt is slightly thinner than those too, as expected. I think the Beefy is the heaviest, if that helps. If Hanes did a 3oz or thinner one I would order that for use as an undershirt in hot weather. The 4.5oz Nano is still a lot thicker than the Hanes short-sleeve undershirts my husband had been wearing before.
One thing you might also want to know is that the Beefy and the Soffe have banded/sweatshirt-style sleeve cuffs, whereas the Nano has simple sleeves just hemmed without a stretchy band. If you prefer sweatshirt-style banded sleeves, choose one of the others, not the Nano. Personally I dislike the look of sweatshirt cuffs on teeshirts.
Re size, they all seem amply sized, as expected. The Soffe Large is about the same physical size as the Nano XL (but the Nano still looks huge nevertheless!). The Beefy XL is wider, and specifically says "preshrunk" on the label. Sleeve length is about the same on all of them. The Soffe is about 0.5 inches longer. I haven't tried washing them at high temperature yet but if they shrink, I will update my review.