Costco started carrying these ultra thin, stretchable crewneck short sleeves shirts. The brand I have is called "32 degrees cool", but I think they have other b

Costco started carrying these ultra thin, stretchable crewneck short sleeves shirts. The brand I have is called "32 degrees cool", but I think they have other brands now like Bench, that sell this same blend of material, black or white color. Compared to an a cotton undershirt the difference in comfort is amazing. Basically you don't feel any of the stitches, or anything pressing on your armpits. And its super light weight. You can sleep in it, its so comfortable. And its also cheap, 3 or 4 pack for under $20.