Glossary

The terms used across this site, defined once. Where a term needs more than a definition, we link to the article that explains it properly.

Waterproofing

Hydrostatic head: the height of a water column a fabric resists before water forces through, in millimetres. Around 10,000 mm handles city rain; 20,000 mm covers pack straps and sitting on wet ground. See ratings explained.
ISO 811: the international standard for measuring hydrostatic head, specifying the rate of pressure increase and water temperature. AATCC 127 is the American equivalent and uses a different rate, so results are not interchangeable.
DWR: durable water repellent, a finish on a fabric's outer face that makes water bead and roll off. It wears off with use and washing and can be reapplied. See how to wash a waterproof jacket.
Wet-out: when the outer face fabric saturates, the garment stops passing vapour outward and your own sweat condenses inside. It feels like a leak and is not one.
Seam taping: bonded tape sealing the stitch holes on the inside of a garment. Without it, a high fabric rating does not describe the finished jacket.
Water resistant vs waterproof: resistant means it copes with light rain for a while; waterproof means it holds out sustained rain under pressure. "Showerproof" is a marketing word, not a standard.

MVTR: moisture vapour transmission rate, in g/m²/24h. Higher is more breathable, but only comparable within a single test method.
JIS L 1099 A-1 and B-1: two Japanese test methods for MVTR. A-1 is the upright cup and returns conservative figures; B-1 is the inverted cup and returns substantially higher ones from the same fabric.
ASTM E96: an American MVTR standard with several procedures, including B and BW, which produce different results from each other and from the JIS methods.
RET: evaporative resistance measured on a sweating hot plate under ISO 11092. Lower is better. It cannot be converted to MVTR.
Vapour pressure gradient: the moisture difference across a fabric that drives breathability. Near zero in hot humid air, which is why breathability underperforms in the tropics.

Hardshell: an uninsulated waterproof outer layer built on a membrane or coating. See softshell vs hardshell.
Softshell: a woven, stretchy, breathable outer layer that resists water rather than blocking it.
Membrane vs coating: a membrane is a separate film bonded into the fabric; a coating is applied directly to the face fabric. Both can be waterproof, and they age differently.
Delamination: a membrane separating from its face fabric, visible as bubbling on the inner face. Not repairable.
Denier: a measure of yarn thickness. Higher denier means heavier, tougher fabric and less packability.
Ripstop: a reinforcing grid woven into a fabric so a tear does not spread.
Martindale: an abrasion test counting rubbing cycles a fabric survives under a set pressure.

Base layer: the garment against your skin, chosen for moisture management rather than warmth.
Mid layer: an insulating layer that traps air, usually fleece or a light insulated jacket.
Shell: the outer layer, chosen for wind and rain, with no insulating role of its own.
GSM: grams per square metre, the weight of a fabric. 150 to 200 is the general travel range for base layers.
Micron: merino fibre diameter. Lower is finer and softer; 17 to 18.5 suits most skin. See merino vs synthetic.
Packability: how small a garment compresses, which decides whether you carry it every day. See packable vs structured.

Garment measurement: the dimensions of the item itself. What VEAR publishes.
Body measurement: the dimensions of the wearer, which a garment must exceed.
Ease: the difference between the two, the room you have to move.
Layering allowance: the extra circumference needed for what goes underneath. See sizing between two sizes.