There are a number of fabrics that show sweat easily. Most of them will show sweat to some degree. However, the kinds of shirts that many people have to wear to a work environment make it easy for the sweat to show. To avoid a sweat stain, there is a way to take advantage of a better type of fabric to keep the sweat from showing through.
A t-shirt is often worn underneath another shirt as a way to keep sweat from going through to the top shirt. This is effective for several reasons. The first is simply that sweat has a lesser chance of showing through two layers of fabrics than showing through only one. This is true of any fabric, even if the top layer is another t-shirt.
The second reason, however, is the reason that people choose t-shirts as their undershirts of choice. Cotton is an absorbent and breathable fabric that will take sweat away from the skin easily. It will allow the sweat to dissipate quickly through the pores in the fabric. This makes it work like a sponge when worn under another shirt and keeps the sweat from going to the outer shirt and being visible to the world.
There are some cases in which this will work better than others, however. If the outer shirt is a little larger than the t-shirt worn under it, the results will be better. This will allow a little air in flow between the two shirts. The air flow will allow the sweat to evaporate more easily and to keep it from seeping through to the outer shirt.
Wearing a tight shirt over the t-shirt or wearing an outer shirt that fits just as closely as the t-shirt will not have the same results. Without even a small layer of air in between the two shirts, the outer shirt will start to show the sweat far sooner than if there is a layer of air.
If the weather is warm, it can be a problem to wear two shirts at the same time. It can actually cause more sweat, making it harder to then hide the sweat. The solution for warm weather days is to wear an outer shirt that is unbuttoned, leaving the t-shirt underneath it visible. This is a casual look that isn’t too warm but will hide any sweat that may occur. This look isn’t always acceptable for the office, but the look can be worn on casual Fridays and to more casual occasions.
Another variation of this in a business casual office is to wear a t-shirt and a loose-fitting button-up shirt on the outside, but with the top few buttons left undone. This is a casual look that can be offset by a formal-looking outer shirt. A clean, starched shirt that has a few inches of t-shirt peeking out from the top will still look business-like enough for most offices. And, it will keep you from being the guy in the office with the sweat stains.