Moisture is extremely bad for cricket bats. Wet bats will often become broken bats, or bats that require extensive repairs.
A favourite bat returned to Laver & Wood to have the toe repaired.
When a bat gets exposed to excess moisture the compressed willow fibres expand. The willow acts like a sponge, as the surface of the bat is incredibly porous. As bats expand the protective harder surface is lost. Bats without the hard facing will be much more likely to crack or split.
Moisture damage occurs often when playing on wet surfaces, or having throw downs with a wet ball. Be particularly wary of artificial pitches or nets, as even if the surface is dry the subsurface may be wet. When the bat is tapped on the pitch moisture will be drawn up and affect the toe of the bat.