Choosing the right carpet underlay has a direct impact on comfort, warmth, noise and how long your carpet lasts. With so many options available, it’s easy to overcomplicate it. In reality, most modern carpet installations will benefit from a PU (polyurethane) underlay, which is now the most widely used and reliable option across UK homes. This guide breaks down what actually matters when choosing underlay, and what to avoid.
Why Underlay Matters for Carpets
Underlay is not just an add-on. It’s what protects your carpet and improves how it feels day to day.
A good underlay will:
- Improve comfort underfoot
- Reduce noise when walking on the floor
- Add warmth and insulation
- Extend the life of your carpet by absorbing impact
Without the right underlay, even a good-quality carpet will wear out faster.
Industry guidance from organisations such as Carpet Foundation and BSI Group also supports the importance of correct underlay selection and installation.
The Best Type of Underlay for Carpet
PU (Polyurethane) Underlay
This is the main type of underlay used today and what we would typically recommend.
It offers:
- Consistent support across the floor
- Good comfort without being too soft
- Strong recovery, meaning it bounces back and protects the carpet
- Suitable performance for most rooms in the home
PU underlay strikes the right balance between comfort and durability, which is why it’s the go-to choice in most installations.
Thickness and Density: What You Actually Need
Thickness matters, but more is not always better.
Typical ranges:
- 8–11mm: Ideal for most rooms. Good balance of comfort and support
- Up to 12mm: Acceptable in lower traffic areas like bedrooms
- 15mm+: Not recommended
Anything too thick can cause excessive movement in the carpet, leading to premature wear, poor fitting and a less stable feel underfoot.
In practice, we don’t tend to recommend anything over 11mm high-density underlay, as this gives the best overall performance.
Matching Underlay to the Room
- Living Rooms and Bedrooms: Comfort is key here. A PU underlay around 9–11mm works well, giving a softer feel without compromising support.
- Hallways and Stairs: These areas take more traffic, so durability matters more than softness. A slightly firmer, high-density underlay is the better choice.
- Underfloor Heating: Use a low tog-rated underlay that allows heat to pass through efficiently. Always check compatibility with both the carpet and heating system.
Noise Considerations
One of the most common issues with carpets is noise.
Using the wrong underlay, especially something too thin or too soft, can lead to:
- Hollow or “drummy” sound
- Increased footstep noise
- Faster wear due to movement
A good quality PU underlay helps reduce impact noise and creates a more solid feel underfoot.
When Should Underlay Be Replaced?
Underlay should not be treated as a one-time install.
Best practice is to replace the underlay every time you replace the carpet.
Reusing old underlay can:
- Reduce the lifespan of the new carpet
- Affect comfort and appearance
- Lead to uneven wear
If you’re investing in a new carpet, replacing the underlay at the same time protects that investment.
Installation Basics
To get the most from your underlay:
- Ensure the subfloor is clean, dry and level
- Lay underlay neatly with tight joints
- Tape seams where required
- Fit carpet correctly to avoid movement
Following manufacturer guidance is key, especially for warranty protection. Many manufacturers, such as Cormar Carpets, provide clear fitting recommendations that include underlay requirements.
Final Thoughts
The best underlay for carpet is usually a high-quality PU underlay in the 8–11mm range. It gives the right balance of comfort, durability and noise reduction. Going too thick can cause more problems than it solves, and reusing old underlay is a false economy. If you get the underlay right, your carpet will look better, feel better and last longer.