Choosing a Coat: Warmth, Waterproofing and What the Ratings Mean

A coat is worn more hours than almost anything else you own and is bought on appearance more often than on specification. The specifications are not complicated once you know which two questions to answer: how cold, and how wet.

Insulation: down or synthetic

• Down — the best warmth for its weight, compresses small, lasts many years with care. Loses most of its insulating ability when wet and dries slowly. Look for the fill power figure, which measures loft quality, and the fill weight, which is how much is actually in the coat. A high fill power with a tiny fill weight is a light coat, not a warm one.
• Synthetic — heavier and bulkier for the same warmth, but keeps insulating when damp and dries fast. Usually cheaper and easier to wash.

The choice follows your climate. Cold and dry favours down; cold and wet favours synthetic, or down under a genuinely waterproof shell.

If buying down, check for a responsible sourcing certification, which is standard on reputable brands.

Waterproofing ratings

Two numbers are usually quoted, and they measure different things:

• Water column, in millimetres — how much water pressure the fabric resists before leaking. Higher is more waterproof.
• Breathability, in grams of moisture passed per square metre per day — how well sweat escapes. Higher breathes better.

A very waterproof, poorly breathing jacket leaves you wet from the inside. For anything active, breathability matters as much as the waterproof number.

Water resistant is not waterproof. It sheds a shower and soaks through in sustained rain.

The details that decide whether it works

• Taped seams. Untaped seams leak regardless of the fabric rating. Fully taped is better than critically taped.
• Hood adjustment, and whether it moves with your head rather than blinding you.
• Storm flap over the main zip, since zips are the usual leak point.
• Cuff and hem adjustment, which controls draughts.
• Pit zips for venting on anything worn while moving.
• Pocket position — pockets under a rucksack hip belt are unusable if you carry a pack.

Length and layering

Longer coats are warmer and restrict movement. Try the size against what you will wear underneath: a coat that fits over a shirt may not fit over a thick jumper, and a coat too tight over layers is colder, because compressed insulation does not work.

Care

The water-repellent finish on outer fabrics wears off and can be reproofed — a coat that has started wetting out is usually not finished, just due for treatment. Down coats can be washed with the right detergent and must be dried thoroughly to restore loft.

Before you order

Check the fill weight as well as fill power on down. Check whether seams are fully or only critically taped. Check the sizing allows your usual layers underneath. And check the care requirements, since a coat needing specialist cleaning carries a running cost.