Have you ever heard the term “breathable paint” and wondered what it means?
It’s not paint that inhales and exhales, but it does allow your walls to breathe – which is great for your home and for you!
Breathable paint lets moisture pass through easily without trapping it inside your walls. Simply put, it absorbs humidity and releases it once the moisture levels have lowered. This helps issues like damp, mould, and peeling paint, which can occur when moisture gets trapped. Allowing the natural moisture that’s in the walls and atmosphere to flow through the walls without damaging the building.
What makes a paint breathable?
Different paints may be tested using different recognised standards. To make things simple, we've outlined the key terms below to help you understand how vapour open a paint is and whether it's suitable for you.
Sd is the most common value, but you may also see breathability expressed as a Moisture Vapour Diffusion (V) value, or a Moisture Vapour Transmission Rate (MVTR) value.
Understanding Sd, MVTR and V values
Steam Diffusion (Sd)
This describes how easily water vapour can move through paint.
- Sd < 0.14m = Class 1, highly vapour permeable
- Sd < 1.0m = generally considered breathable
The lower the Sd value, the better.
Moisture Vapour Diffusion (V)
This measurement describes how readily moisture vapour diffuses through a material, it can be used to calculate an Sd value.
While presented differently, V and Sd both describe vapour diffusion performance, helping to indicate how resistant a coating is to moisture vapour movement.
Moisture Vapour Transmission Rate (MVTR)
The MVTR measures how many grams of water vapour can pass through a surface over 24 hours, giving a clear indication of real world moisture movement.
Unlike Sd and V values, which describe vapour diffusion characteristics, MVTR measures the actual quantity of moisture vapour transmitted over time.
- MVTR is usually expressed in g/m²/24h
- A higher MVTR value indicates greater vapour transmission and improved breathability performance
Why all three values matter
Although these measurements are related, they do not describe exactly the same thing:
- Sd and V values describe vapour diffusion = how easily moisture moves through the paint, ensuring moisture isn't trapped behind the paint
- MVTR describes vapour transmission = how much moisture passes through the paint over time, ensuring moisture can move through efficiently
It’s possible for a paint to have a low Sd value (low resistance) but still not move large amounts of moisture quickly. Equally, a product might allow higher vapour movement but still create some resistance.
True breathability is a balance of both.
For interior spaces, where humidity fluctuates daily (cooking, showering, drying clothes), assessing both values gives a much more accurate picture of how a paint will perform in helping to protect walls from damp and condensation.
As an added bonus, our Claypaint is a hygroscopic paint because of its high clay content. This means that it will even out the humidity in a room by absorbing excess moisture, and release it when the moisture conditions return to normal.
This may make your wall colour appear darker when moisture is being absorbed, but once dried, it will return to its original shade.
How do I know a paint is breathable?
Along with 'eco friendly', 'breathable' has become a popular word in the paint world - and while all paints are breathable to a certain point, it’s important to know how breathable.
There are two simple ways to tell if a paint is breathable – the steam diffusion (Sd) value or the V value, and the Moisture Vapour Diffusion Rate (MVTR).
For a paint to be classed as breathable, it should have an Sd value of 1 or lower. The lower the value, the less resistance it creates and the more breathable the paint.
For example, our Claypaint has an Sd value of 0.02m, which means it has exceptional breathability and responds easily to variations in humidity.
The Moisture Vapour Transmission Rate (MVTR), measures the amount of water vapour in grams that can pass through over a 24 hour time period. In this case, the higher the value, the better.
Our Claypaint has a MVTR value of 1115g/m² per 24 hours, compared to a typical emulsion paint, which usually measures between 400 – 500g/m².
What is the most breathable paint?
Our Claypaint is the most breathable interior paint in our range of finishes and is perfect for painting over lime plaster as well as standard plaster or even previously painted surfaces. A diluted coat of Wall Glaze can be used for added durability without affecting Claypaint’s breathability.
Our Silicate Masonry Paint is the best breathable paint for exterior mineral surfaces. It’s especially suitable for lime render but can be used on brick, stone, cement, concrete, pebble dash and plaster.
For our Silicate Masonry Paint to work effectively, it needs to be used with one of our primers. Silicate Primer to create a permanent chemical bond with bare porous mineral surfaces, or Bonding Primer to create a strong mechanical bond with existing sound, previously painted masonry surfaces.
Is emulsion paint breathable?
Not all emulsion paints are breathable. Most standard emulsions contain vinyl and acrylics that create an impermeable layer on the surface.
This layer acts as a barrier that traps moisture or prevents water vapour from passing through easily. However, some emulsion paints are specifically formulated to be breathable, often using ingredients like clay, which naturally supports moisture movement.
Find out more about breathable paints on our breathable paint hub.
