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?
The breathability of a paint is normally measured by its Sd (Steam Diffusion) value which gives an idea of the water vapour resistance. The lower the Sd value, the more breathable the paint is.
For example, our Claypaint has an Sd value of 0.02m, which means it has exceptional breathability and responds easily to variations in humidity.
However, Sd value on its own does not give the full picture of breathability. It tells you how easily vapour can pass through, but not how much moisture actually does move through the paint over time.
That's where additional measurements come in, such as MVTR (Moisture Vapour Transmission Rate) and Moisture Vapour Diffusion (V) values.
- Sd value = resistance to vapour (lower is better)
- MVTR value = amount of vapour movement (higher is better)
- V value (moisture vapour diffusion) = another way of expressing how much vapour passes through
Understanding MVTR and V values
The MVTR measures how many grams of water vapour can pass through a surface over 24 hours (g/m²/24h), giving a clear indication of real world moisture movement.
Sometimes, instead of MVTR, manufacturers use a Moisture Vapour Diffusion (V) value. This represents essentially the same performance characteristic: how much moisture vapour can move through a coating. But it may be expressed using different standards or testing methods.
Because of this, MVTR and V values are often interchangeable in purpose, even if they are presented differently on technical data sheets.
Whether labelled as MVTR or V value, a higher figure always indicates better moisture movement and improved breathability performance.
Why both Sd and MVTR (or V) matter
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.
- A low Sd value ensures moisture isn’t trapped behind the paint
- A high MVTR or V value ensures moisture can pass through efficiently in real conditions
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 and the moisture vapour diffusion rate (MVTR) or V value.
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.
The moisture vapour transmission (MVTR) or V value, 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.
