Merino wool is an active fibre that reacts to changes in body temperature. So it helps you stay warm when the weather is cold, and cool when the weather is hot.
Merino wool can absorb moisture vapour which means less sweat on your body. Merino wool even absorbs the odour molecules from sweat, which are only released upon washing.
The fibres are extremely fine, enabling them to bend far more than traditional, coarser wool fibres. This makes Merino wool feel soft and luxuriously gentle next to your skin.