Sisal is the traditional material used for modern competition dartboards.
Sisal is a strong natural fibre obtained mainly from the leaves of the Agave sisalana plant. Dartboards made from compressed sisal fibres can close around holes after darts are removed, allowing the surface to remain playable for a long time.
Earlier dartboards were made from materials including elm wood, clay and coiled paper. Those surfaces had different maintenance problems: wooden boards could dry out and split, while paper boards wore more quickly.
A sisal board is not self-healing in a literal sense. The fibres shift back together, and rotating the board regularly helps distribute wear. Professional boards also use a blade-style wire system to reduce the amount of surface blocked by metal dividers.