Size of an Inner Layer
The inner layer sizes used for layered clothing are small (S), 
medium (M or MD), large (L), extra large (XL) and even higher. Sometimes these letters are replaced by numbers like 8, 10, 12, 14 and so on. The numbering sequence corresponds to the letters (i.e., S is 10, M is 12 and so on). The inner layer is also known as a base layer.
Purpose
The function of the inner layer is to keep the perspiration away from the person’s skin and onto the succeeding layers. The effect should make the person feel more comfortable and warmer.
Regardless of the inner layer size, the transfer will occur because of capillary action. This is also known as wicking and the parts are called wicking materials. After the moisture has gone from the skin to the non-absorbing layer, it gets more surface area.
This will result in faster evaporation. Only clothing that adequately handles moisture transfer can be called an inner garment. If it cannot, it is known as a mid-layer garment.
Fabrics and Materials
There are many choices available. Some of the most ideal are microfiber-based fabrics and polyester. What makes them ideal is they transfer moisture easily without absorbing the moisture.
Wool is also a good choice for various inner layer sizes because of its wicking capabilities. However, there are various wool types, with some comfortable and others rough. One advantage of wool is that it doesn’t generate smell as rapidly as other materials.
Some inner layers are made from silk. While they are comfortable, they are not as resilient. Maintenance is also high, so it isn’t used that much.
Cotton is another favorite mainly because it is cheap. The drawback is that it can soak in moisture. It can also be difficult to dry out. For this reason, some prefer to use cotton as a middle or insulating layer.
Other Considerations
Because the base layer is the first layer you’ll wear, it’s important to find fabric you are comfortable with. Ensure the fabric is breathable so you don’t feel clogged up. A versatile inner layer can also be worn during any season and still make you feel comfortable. The good ones can also be worn during work.
The inner layer size you choose, plus the fabric is crucial. By picking the right combination, sweat buildup can be avoided whether you are running, cycling or engaged in other strenuous activities.
