Best Underlay for Underfloor Heating: 2025 Expert Review
DR Joinery
Expert Joiner & Flooring Specialist
Installing underfloor heating (UFH) is a significant investment, especially here in York where we are constantly battling the damp and draft of historic housing stock. However, I often see homeowners undo all that good work by choosing the wrong underlay. It is the single most common reason for an inefficient system.
The challenge with hardwood or engineered flooring over UFH is balance. You need an underlay that cushions the wood and dampens sound, but also has a low enough 'TOG' rating to let the heat pass through. get this wrong, and you effectively insulate your room from the heating source, leading to high bills and cold feet.
In this review, I've selected three products that serve different roles in the UFH system: a budget-friendly insulation board for the base layer, a luxury acoustic foam for specific setups, and a dedicated low-TOG underlay that I typically recommend for floating timber floors.
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Specs vs. The Real World
The Spec: "TOG Rating Claims"
"Higher TOG usually means better insulation, which sounds positive."
For UFH underlay (placed *above* the heating element), you want the opposite. Ideally, a TOG of less than 0.5. Anything higher acts as a barrier, trapping heat under the floorboards rather than warming the room.
The Spec: "Thickness vs. Stability"
"Thicker underlay (10mm+) feels more luxurious and softer to walk on."
With floating wood floors (click-lock), too much 'bounce' from thick foam can cause the locking joints to snap over time. For timber, a denser, thinner underlay (3-5mm) is often structurally safer than a soft 10mm foam.
My Top 3 Recommendations
Three options to cover different needs and budgets
XPS Foam Insulation Boards Floor Underlay 800 x 600 x 5mm
IMPERIAL STUDIOS
This is crucial to distinguish: these XPS boards are primarily designed as *insulation boards* to go beneath your heating system, not necessarily as the top layer under the wood. With a high TOG of 2.15, they are excellent at stopping heat escaping downwards into the concrete, making your system far more efficient.
The Good
- Excellent thermal barrier to stop heat loss downwards
- Waterproof and mould resistant - ideal for York cellars
- Lightweight and easy to cut with a craft knife
The Bad
- Too insulating to use *above* the heating elements (would block heat)
- Requires a flat subfloor as boards are rigid
Installer Tip:
Use these boards directly on your concrete subfloor, *underneath* your electric heating mats or pipes. This forces the heat upwards into the room. Do not place these on top of the heating element if you want the room to get warm!
Priced at £21.90 at the time of writing
Check Price on AmazonNassboards Thermal Underlay for Underfloor Heating – 10mm Flame-Retardant Foam
Nassboards
If sound reduction is your priority, this Nassboards option offers an impressive 46 dB reduction. It features airflow holes to allow heat transfer despite its 10mm thickness. It provides a very plush feel, but as a joiner, I advise caution when using this with certain click-lock wood floors due to the thickness.
The Good
- Excellent noise reduction - perfect for upstairs flats
- Airflow holes help heat transfer despite the thickness
- Flame retardant and Formaldehyde-free rating
The Bad
- 10mm is very thick - may affect door clearances
- High cost compared to standard foams
- Might be too soft for some thin laminate/wood joints
Installer Tip:
Before buying, check your floor levels. This adds 10mm plus your floor thickness. In many York terraces, this might mean planing down doors or adjusting skirting boards. Also, confirm your wood flooring manufacturer approves a 10mm underlay.
Priced at £149.99 at the time of writing
Check Price on AmazonGrandismo® Underfloor Heating Underlay/Underlayment for Vinyl - Wood - Laminate
Grandismo
This is the 'problem solver' for heat transfer. With a TOG rating of just 0.35, it offers minimal resistance to heat, ensuring your system runs efficiently. It is specifically designed for wood, laminate, and LVT, providing the right balance of support and conductivity.
The Good
- Extremely low TOG (0.35) for maximum heat efficiency
- Designed specifically to support hard flooring types
- Decent sound reduction (17dB) without being too thick
The Bad
- Thinner profile hides fewer subfloor imperfections
- Not as plush underfoot as the 10mm options
Installer Tip:
This is my go-to type specifically for floating engineered oak floors over UFH. It allows the heat to penetrate the timber quickly without 'cooking' the bottom layer. Ensure you tape the seams with vapour tape to create a moisture barrier.
Priced at £33.50 at the time of writing
Check Price on AmazonFrequently Asked Questions
What is the ideal TOG rating for underfloor heating underlay?
Can I put underlay under electric heating mats?
Does thickness matter for wood flooring underlay?
Do I need professional installation for an underfloor heating floor?
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