Wool
Merino, mohair, alpaca or cashmere... Wool is a living, self-cleaning and delicate material. It doesn't like heat or sudden movements.
The wash
Wool hates water! Simply air your jumper after wearing it. For washing (1 to 2 times per season maximum), opt for hand washing in lukewarm (or even cold) water, or a "Wool/Hand wash" machine program on cold, with no spin (or 400 rpm max).
Detergent: Use a special wool detergent, in small quantities. No fabric softener, which weighs down the fibres.
Drying
Flat exclusively, on a terry towel, away from any direct heat source or sunlight. Hanging a wet sweater would permanently distort its shape.
Expert advice
Pilling is a natural phenomenon caused by friction, especially on new knits. Use a fabric shaver or a cashmere comb with care to restore their new appearance.