If you are talking about the heattex turtle shirt, they are very thin but work well for their purpose especially if you keep the size on the tight side to keep it close to your torso, but wear as an outer shirt? I wouldnt.
I disagree with the general consensus of lambswool. I bought 4 of the sweaters and wear them daily over my dress shirts. I've worn 2 of them at least 10 times each with little to no pilling.It's a $21 dollar sweater. If it only lasts 20 wears, that's a buck a pop.I think it's much warmer and slightly thicker then Merino, which I also own.For what it's worth.
I think they are really nice. I got the V neck versions and they are perfect in a M to layer over a dress shirt. The white is a little transparent, but the darker colors are fine and are actually warm. For $21 or whatever they are, you can't go wrong.