Updated December 2025 by the Crib Goch Outdoor team — based on real wet-weather experience in Eryri. When buying tents, jackets or camping gear, you’ll often see the term Hydrostatic Head (HH) thrown around. But what does it actually mean — and how waterproof is 2000mm, 5000mm or 10,000mm in the real world? This updated guide explains HH in simple terms, how to compare ratings, and what level of waterproofness you really need for UK…