Rain jacket listings are full of numbers and labels: 5,000mm, 10,000mm, "showerproof", "water resistant", "fully taped seams", "breathable". If you just want to stay dry on the walk to the station, it's hard to know which matters. This article explains the terms in plain English and what they mean for typical UK weather.
Water resistant, showerproof and waterproof
These words aren't interchangeable, even if sellers sometimes treat them that way.
- Water resistant or showerproof usually means the fabric has a coating or a durable water repellent (DWR) finish that makes rain bead up and roll off. It copes with light drizzle and short showers, but steady rain will eventually soak through, especially at the shoulders where bag straps press the fabric.
- Waterproof should mean the fabric itself stops water getting through under pressure, usually thanks to a membrane or coating, and that the seams are sealed. A truly waterproof jacket keeps you dry in sustained rain.
If a listing only says "water resistant", assume it's for drizzle, not for a 40-minute walk in a downpour.
What the "mm" number means
The figure in millimetres is the fabric's hydrostatic head. In a test, a column of water is placed on the fabric and the height is increased until water starts to come through. A 5,000mm rating means the fabric held back a 5,000mm (five metre) column of water before leaking.
Higher numbers mean the fabric resists more pressure. Pressure comes from heavy rain, wind driving rain into the fabric, and anything pressing on it: rucksack straps, sitting on a wet bench, or kneeling.
As a rough guide used across the outdoor industry:
- Lower ratings (around 1,500 to 5,000mm): fine for light rain and short periods outside.
- Mid ratings (around 5,000 to 10,000mm): a sensible level for everyday UK commuting and walking in moderate rain.
- Higher ratings (10,000mm and above): better for prolonged heavy rain, hillwalking or carrying a heavy bag.
These bands are approximate, and test methods differ between brands, so use the number to compare jackets rather than as a guarantee. Many budget jackets don't state a rating at all; that doesn't always mean they're poor, but you have less to go on.
Seams matter as much as fabric
A jacket with excellent fabric will still leak if water gets through the stitching. Every stitch is a tiny hole.
- Fully taped or sealed seams have waterproof tape applied over every seam on the inside. This is what you want for real rain.
- Critically taped seams only cover the most exposed seams, such as shoulders and hood. A compromise.
- No taping means the jacket is effectively water resistant, whatever the fabric rating.
Also look at the zip. A storm flap over the main zip, or a water-resistant coated zip, stops rain getting in at the front.
Breathability: why you can feel wet in a waterproof
If you've ever arrived somewhere in a "waterproof" coat with a damp shirt, it may not have leaked. It may be condensation. When you walk briskly or cycle, your body produces heat and moisture. If that moisture can't escape, it condenses inside the jacket.
Breathable fabrics let some water vapour out while keeping rain out. Some listings give a breathability figure in grams (g/m²/24h); higher means more breathable. Cheaper waterproofs often breathe less, so they feel clammy on a fast walk.
Practical ways to reduce condensation:
- Open the front zip a little or use pit zips if the jacket has them.
- Wear a thin, quick-drying layer underneath rather than cotton.
- Slow down slightly on the way to the station.
The hood is the most important feature
For British drizzle and sideways rain, a good hood matters more than an extra few thousand millimetres. Look for:
- A peak or stiffened brim that keeps rain off your face.
- Adjusters at the back and sides so the hood turns with your head instead of blocking your view.
- Enough room for a hat underneath in winter.
Keep a waterproof working
The DWR finish on the outside wears off with use and washing, making the fabric "wet out" and feel damp even when it isn't leaking. To keep it working:
- Wash it occasionally with a technical wash rather than normal detergent and fabric softener, which can clog the fabric.
- Re-proof it with a wash-in or spray-on product when water stops beading.
- Follow the care label; some finishes are reactivated by a low tumble dry.
Umbrella or hood?
An umbrella keeps your head and shoulders dry, but is little help in wind and leaves your legs exposed. A good hood with a peak handles sideways drizzle better and leaves your hands free. For a windy coastal or exposed walk, a jacket and hood usually beats an umbrella; for a still, heavy downpour on a short walk, an umbrella over a water-resistant coat is fine.
What to buy for typical UK use
- Short walks to the car or bus: a lightweight water-resistant or entry-level waterproof shell is enough.
- Daily walking commute or school run: a jacket that says waterproof with taped seams and a decent hood; mid-range ratings are plenty.
- Cycling or long waits outside: prioritise breathability, a longer back hem and reflective details.
- Hillwalking: a higher rating, fully taped seams and a proper adjustable hood are worth paying for.
Our rain jackets under £40 guide applies these tests to budget jackets, and wet commute kit under £30 covers the rest of the kit: bag covers, umbrellas and shoes. For staying warm as well as dry, see how to layer for a cold, wet UK commute.