What you wear next to your skin has a great effect on how your layering system will perform.
Synthetics: This category includes the best wicking and fastest drying fabrics in the world. For aerobic activities especially, a good synthetic baselayer will prove to keep your core temperature from plummeting, and will dry the quickest in wet conditions to maintain insulation.
Merino wool: In the last few years, Merino has made a huge impact on the outdoor world. Originally sold for fine suiting material, this extra soft, non-itch wool is the most breathable of our base layer fabrics, meaning that it has a regulatory effect on body temperature, and a wider comfort range than either synthetic or silk. Though wool dries the slowest, it maintains most of its warmth when wet, and is able to absorb moisture from the skin more readily than anything else, keeping your skin from feeling cold and clammy. Come try on an Icebreaker Merino base layer today!
Silk: These base layers are best suited for moderate climates and non-aerobic activities. Silk absorbs less moisture than cotton, but cannot insulate as well as wool while wet.