Sizing simply by chest circumference in centimetres, with the comparable easy size in the brackets. These have a snug fit and no different length sizes - they fit most people and stretch quite a lot.

The fabric consists of 50 % kermel and 50 % viscose. Basically this means that the shirt won't easily catch fire and even if it does, it does not melt on your skin. The viscose works sort of like wool; transfers moisture away from the skin, doesn't lose all of its warmth when wet, and dries pretty quickly. In other words, this is a nice quality technical underwear. 

Wash at 40 degrees Celsius / 104 degrees Freedomheits.