What is cobweb mould and how do I treat it?

Cobweb mould is a grey, wispy growth that spreads across a substrate surface much faster than mushroom mycelium and looks fluffier and greyer. It is one of the few contaminants that is sometimes treatable: caught early, misting the spot with 3% hydrogen peroxide and increasing fresh air exchange can stop it. Lower the humidity slightly and improve airflow to prevent it.