What 550 gsm actually means

Most bag marketing is adjectives. Rugged. Premium. Bombproof. None of these are measurements, and a company that only offers adjectives is usually hoping you won't ask for numbers.

The four numbers worth knowing

• —GSM — grams per square metre. Fabric weight. 550 gsm tarpaulin is heavy enough to hold structure and shrug off abrasion without turning the bag into luggage you resent carrying.
• —Hydrostatic head — how tall a column of water the fabric holds before it leaks. Above 2,000 mm you are fine in sustained rain. A 'water-resistant' claim with no number attached usually means under 500.
• —Denier — thread thickness. Useful, but widely gamed: high denier in a loose weave is weaker than lower denier woven tight.
• —Cycle count — how many times a zipper opens and closes before failure. Zippers are where bags die. Ours are specified to a 2,000-cycle test. The result gets published when the sealed sample is tested.

None of this is exotic knowledge. It is simply the information a maker has and usually declines to publish, because published numbers can be checked.

Specificity is a promise. Adjectives are a hope.