An undershirt that does not show through your shirt
Short answer: Choose a skin toned style with a v neck and a close fit. A white undershirt under a white shirt is the most visible choice of all.
Colour matters more than you think
White fabric under white fabric creates a clear contrast, because one layer is denser than the other. An undershirt in a skin tone disappears instead, because it resembles the skin in the light that passes through.
The neckline
A crew neck peeks out of the shirt opening. A v neck or a deep round neck stays below the top button. That is the detail that most often gives an undershirt away. See bamboo undershirts for men.
The fit
An undershirt should sit close to the body. If it is loose, it folds under the shirt and shows as lines. Choose a style with a little elastane in your normal size. See bamboo underwear for men.
The length
The undershirt has to be longer than the shirt is short, meaning well below the waistband. Otherwise it rides up and forms a roll at the waist. See bamboo shirts for men.
Frequently asked questions
Why wear an undershirt at all
It takes the sweat so the shirt stays dry, and it extends the shirt's life.
Does an extra layer not make it warmer
In bamboo viscose rarely. The layer moves moisture and cools more than it warms.
Can I use a tank top instead
Yes, but it does not cover the armpit, where sweat is heaviest.