Base Layers basically refer to the primary clothing pieces that are used as foundationsfor the overall ensemble. These layers are what everything else in the ensemble is then built upon. They are meant to be put on under extra layers, like fleeces or long-sleeved tops.
Aside from making you more comfortable in different weather conditions, these layers are also worn to get rid of the sweat on your body, and make you feel dry or warm as needed.
Thanks to the wicking process, base layers can suck up moisture. See, whenever moisture leaves the skin to go onto the layer, the surface area becomes greater, as well, causing the moisture to evaporate faster. This will leave you more comfortable and much drier than you would normally be. Also, the quicker the moisture transfer from one place to the next, the more effective your layer will be in the end - remember that.
These layers consist of various materials, each of which have different benefits and properties. Here are several wicking materials that base layers normally use:
Synthetic layers are made out of polyester, which is beneficial because it can transfer moisture in a highly effective manner. However, it cannot absorb the moisture too well. Plus, polyester tends to be more expensive compared to other materials out there.