Can you please expand on this a bit for me?
Because anywhere in the world I go that's hot, cotton has always been my first choice for comfort. It's always worked for me. Have I simply been lucky all these decades?
Clothing made from natural fibers such as wool and cotton are popular in cooler climates because they can help keep the body warm even when wet. A good wool blanket is a staple of many cold weather endurance kits. Before I go any further, I'm not saying that a 100% cotton shirt or even a wool shirt is sufficient all by themselves. These natural fabrics tend to absorb moisture and tend to stay wet for a long time because the sweat is not transferred to the outside of the garment where it can quickly evaporate. These fibers act like a sponge and soak it all up until they can't hold anymore. We'll ignore the thread weight and weave in this discussion even those these two factors do play a role in the overall evaporation rate of the garment.
The term moisture wicking was coined by the athletic clothing manufacturers to describe a type of blended fabric that moves moisture from the skin to the exterior of the garment so that it can evaporate. We know that the process of evaporation has a cooling effect because the process of evaporation requires heat to convert liquid to a gas. This is why our body sweats, to increase the rate of cooling when we overheat. Clothing acts as an impediment to evaporation. Being naked is best.
Natural fibers are better known for their propensity to retain heat even when wet. It is however, the reluctance of natural fibers to release their water content easily that works against us in hot climates. Being dry and cool is better than being wet and feeling cool/clammy.
In cold temperatures, being wet can quickly lead to hypothermia. Many a hiker has cursed the choice to wear jeans on a winter hike if they happen to get wet...jeans just don't ever dry in the cold without a fire.
On really hot days if I am going to be outside for a long period of time, I prefer lighter fabrics than cotton shirts. I prefer silk because it is so light it's as if you are wearing nothing at all, wicks moisture and is so thin that any sweat evaporates in no time at all. If I am just popping into the car for a quick trip to the store or watching tv I have lots of cotton as my second favorite choice. To wear here in the DR I look for cotton T-shirts that contain 10% - 20% polyester or nylon to help the shirt give up the moisture quicker and easier. Clothing with a high percentage of polyester or nylon are much cooler than cotton, but I find these make me itch so I won't wear them even if they are cooler and more durable than cotton.
I don't wear silk shirts to cut the grass or fix the moto because it snags easily and can be difficult to clean, so a cotton blend it is. I can tell the difference between a 100% cotton shirt and a blended cotton shirt by the amount of water I can wring out of one. You can tell the people wearing cotton around town by the big dark wet areas on their chest and back.
Summary: Cotton or wool shirt in the DR? Obviously cotton. Cotton however is not the best possible choice of material that is available to stay cool and comfortable but a blended cotton can be a good choice for activities where increased durability and ease of cleaning are a consideration.