I got these shirts for my dad. Love him to death but he has a bit of a sweating problem that needed some serious attention :) haha. He works as a doctor so he wears dress shirts a lot of the time when he's seeing patients throughout the day. He's always worn an undershirt when he's working, and not working, but with those dress shirts, especially on warmer days in an office you tend to sweat and sweat tends to soak through your clothes and is then visible. He use to wear the regular cotton material undershirts but those would just end up getting wet and yucky by the end of the day, so I did some research for him and found these!!! They work amazing and he loves them. He says they're extremely lightweight and comfortable and unlike his other undershirts, when he sweats he doesn't feel the wetness of the sweaty shirt on his body all day. He doesn't even notice this undershirt is there! And the nicest part about the shirts is that they keep there nice pure white color! Even if you do mix your laundry load with colors and darks these will stay white and look nice under thinner/light color shirts! I ordered a large for him and that fit him perfectly. He was also a large in the regular undershirts!