What Does Our Breathability Rating Actually Mean?

You’ve spotted “15k” next to breathability on your favourite Proviz jacket. But what does that number really mean — and how does it affect your run or ride on a wet autumn morning? Here’s everything you need to know.

The Basics

Breaking Down the Rating

When you see a breathability rating like 15k on a Proviz jacket or gilet, it refers to a standardised measure called MVTR (Moisture Vapour Transmission Rate). The number tells you how many grams of water vapour can pass through one square metre of fabric in a 24-hour period.

So a 15k rating means 15,000 grams of moisture vapour can escape through every square metre of the fabric each day. In simple terms, sweat vapour generated by your body has 15,000 grams’ worth of “escape route” before it starts to build up inside your jacket.

15,000 grams per m² / 24hrs — what “15k” means
This is how much moisture vapour (sweat) the fabric can transmit outward before you start to feel clammy inside your jacket. The higher the number, the harder the fabric works for you.

You’ll almost always see breathability and waterproofing listed together — for example, 15k/15k on the Solaris jacket. The first number is the waterproof rating (hydrostatic head), and the second is the breathability rating. Both use the same scale but measure completely different properties of the fabric membrane.

The Scale

How Does 15k Compare?

Not all jackets are created equal. Breathability ratings span a wide range, and where a garment sits on that scale should match the intensity of your activity.

5k–10k (Everyday)
Suitable for low-intensity activity or casual outdoor wear. Fine for a commute or a walk, but may feel clammy during sustained effort.

10k–20k (Active Sport - Proviz Range)
Where most serious running and cycling jackets sit. A 15k rating comfortably handles sustained aerobic effort in mixed weather.

Our jackets and gilets are engineered to sit firmly in that active sport sweet spot — delivering high breathability without the ultra-premium price tag.

Runners vs Cyclists

Why It Matters Differently For Each Sport

Breathability isn’t one-size-fits-all. Heat, sweat, and airflow vary between sports — especially running vs cycling.

Runners – Continuous High Output
Running generates sustained body heat. Your core temperature rises quickly and stays high, meaning you’re producing sweat vapour almost immediately. A 15k rating helps vent that moisture efficiently, preventing overheating during longer efforts. Without it, even waterproof jackets can feel like a sauna.

Cyclists – Variable Effort & Wind Chill
Cycling involves fluctuating effort — climbs and descents — plus wind chill. A 15k rating helps manage sweat on climbs while waterproofing protects you during fast, wet descents. Gilets especially benefit from strong breathability since your core works hardest.

“The best waterproof jacket is one you forget you're wearing — and breathability is what makes that possible.”

The Full Picture

Breathability Doesn’t Work Alone

A high breathability rating is just one part of overall comfort. It works alongside:

Underarm & back ventilation panels — boost airflow during high-intensity efforts
4-way tricot stretch fabrics — reduce restriction and improve moisture movement
Seam-sealed construction — prevents water ingress while allowing vapour out
Adjustable cuffs and waistbands — help regulate your internal temperature
Lightweight membranes — reduce trapped heat and improve overall breathability

Quick Reference: What to Look For

When choosing a jacket or gilet:

Commuting or casual riding — 10k is great
Regular running or cycling — aim for 15k
High-intensity training — 15k+ with ventilation features
Gilets — prioritise breathability (core sweat zone)
Year-round use — prioritise breathability as much as waterproofing

The Bottom Line

Stay Dry From Both Sides

A great performance jacket keeps rain out and sweat out. Waterproofing handles the outside; breathability handles the inside.

A 15k rating means the fabric is actively moving 15,000 grams of moisture vapour per square metre away from your body — helping you stay dry, comfortable, and focused.

At Proviz, that balance is at the core of every jacket and gilet — because visibility is only half the story. Comfort keeps you moving.