After training or a long ride, you should hang your numnah up to dry - preferably with the underside facing up. This stops sweat stains from forming and allows the numnah to air out well. When dry, horse hair on the underside can also be brushed off easily. This is the best way to preserve the numnah's colour and shape.
Always follow the washing instructions on the label if washing the numnah in the washing machine.