What makes merino different from many other types of wool is the fineness of its fibres. Finer wool fibres are closely linked with comfort and softness, while the opposite is true for thicker wool fibres.
However, wool quality varies even within Merino sheep, which means some merino is finer than others. Merino wool is therefore not one fixed thing, but a whole family of wool types with different levels of softness and performance.
Another reason merino is so loved is that it tends to smell less than many other materials, including cotton. Wool does not kill bacteria outright, but it does affect how bacteria sit on the fibre surface.
In other words, wool changes the conditions that bacteria prefer. That helps explain why merino often stays fresher for longer. Odour usually develops when sweat, moisture and microbes work together – and wool helps slow that whole process down.
I love it. I wish I knew of it decades ago.