Underlay FAQS: installation, costs and the best choices

Click on the links below to jump to the relevant question:

  1. Is there a step-by-step guide to laying underlay?
  2. How can I ensure I choose thermal underlay?
  3. What’s the best underlay for carpet tiles?
  4. What’s the best underlay for felt carpet?
  5. Does vinyl flooring need underlay?
  6. How thick should underlay be for laminate flooring?
  7. What does carpet underlay do?
  8. Does carpet need underlay?
  9. How much does carpet underlay cost?
  10. Can carpet underlay be used for laminate flooring?
  11. How thick should carpet underlay be?
  12. How can I ensure the underlay won’t cause my doors to drag?
  13. What underlay density should I choose?
  14. What’s the best choice for thick underlay?
  15. Which way up does carpet underlay go?
  16. How long does carpet underlay last?

1. How to lay underlay

Replacing underlay and carpet is simple, provided you have the right tools and take the time to prepare the floor properly before you start.

If you’re not experienced in underlay and carpet fitting, it may be quicker and more cost-effective to get the professionals to do it. You can claim FREE underlay and carpet fitting from United Carpets & Beds when you buy the same amount of Airstep or Treadmore underlay as carpet.

Step 1—prepare the floor and gather your tools

Sweep and vacuum the floor and remove any staples or nails from the carpet and underlay you’re replacing. If you can’t remove nails or staples, hammer them into the floor until they are flush.

For a successful installation you will need:

  • Knee pads
  • Heavy-duty gloves
  • A tape measure
  • A utility knife
  • Underlay tape
  • Heavy-duty staple gun and staples
  • A hammer
  • Carpet grippers

Step 2—measure the room

Measure the room at its widest and longest points and add at least 10 cm to each measurement to allow for trimming and fitting.

Step 3—fit the carpet grippers

Fit carpet grippers around the perimeter of the room (excluding the doorway), ensuring the side the pins in the gripper are angled to face the skirting board. Be sure to leave a gap of around 6 mm between the gripper and the skirting board.

Step 4—roll out the underlay and fasten to the floor

Roll out the underlay so that its edge meets the edge of the carpet gripper. Then fix the underlay to the floor with your staple gun, stapling around every 30 cm. Cut the roll of underlay at the opposite side of the room so it’s a few centimetres over the carpet gripper, then trim so the underlay is flush with the edge of the grippers. If you’re fitting to a concrete floor, we recommend using our carpet adhesive spray.

You’re now ready to fit your carpet!

2. How can I ensure I choose thermal underlay?

All types of underlay will provide some thermal protection against the cold. You can find out the thermal properties of underlay by looking at the TOG measurement. The higher the TOG, the more insulating the underlay.

Where available, United Carpet and Beds include TOG ratings on our carpet materials too, so you know how insulating your carpet is.

The level of thermal rating for carpet underlay will largely depend on what you’re laying the underlay on. Concrete floors tend to be much cooler than wooden floorboards so if you’re laying a carpet on a concrete floor, choose a higher TOG underlay for the maximum thermal benefits.

Best thermal underlay:

Floor type

Product name and image

TOG rating:




Airstep Diamond underlay


£15.99 m²

Buy this underlay now


Woodtex Laminate Underlay


£7.99 m²

Buy this underlay now

3. What’s the best underlay for carpet tiles?

Carpet tiles do not require underlay as they usually have a backing that does the same job. Using underlay with carpet tiles may actually prevent them from staying in place as tiles need to be laid on a flat, even surface.

The soft surface of underlay could cause the tiles to lift up at the edges, making the flooring look unsightly and creating a potential trip hazard.

If you are looking to purchase carpet tiles for the office, you can find out more information by visiting our guide: office carpet and buyer’s guide

4. What’s the best underlay for felt carpet?

Felt-backed carpets do not require underlay, and so are ideal if you’re buying carpet on a tight budget. Felt-backing provides comfort underfoot as well as protection for your carpet pile. However, to maximise the longevity of your carpet and for the ultimate comfort, it’s a good idea to fit underlay underneath a felt carpet.

If you choose to do this, opt for a less expensive underlay which isn’t as thick, as the carpet already has underlay built in. The Airstrip Super underlay is the ideal choice.

Best underlay for felt carpets: Airstep Super underlay

Airstep Super underlay

Thickness: 8 mm

PRICE: £9.99 m²

Buy this underlay now

5. Does vinyl flooring need underlay?

vinyl flooring doesn’t require underlay as it already comes with a cushioned backing which can be fitted directly onto the floor. Vinyl is sometimes called cushion flooring for this very reason.

United Carpets and Beds do not recommend underlay with vinyl, as this can cause weak point in the vinyl. If you are fitting vinyl onto concrete, we recommend you have a screeding treatment on the sub-floor first, to act as a moisture barrier. Screed is used to level out a concrete sub base and provides a smooth and even finish that is better for laying flooring.

You can find out more about vinyl, laminate and hardwood flooring by visiting our guide: carpet, vinyl, laminate and hardwood; which flooring is best for you?

6. How thick should underlay be for laminate flooring?

Underlay for laminate flooring is usually 3 mm thick. This may seem thin, but using thick underlay will create too much bounce when people walk on it and cause the floor to move underfoot.

7. What does carpet underlay do?

Underlay increases comfort and saves you money by:

  • Protect the carpet from excessive wear
  • acting as a cushioning layer that provides ‘spring’ when you walk
  • reducing friction between the carpet backing and the floor
  • helping flooring look better for longer by reducing marks on the carpet left by furniture
  • dampening noise
  • preventing heat from escaping

8. Does carpet need underlay?

Yes, All carpets apart from felt-backed carpets should have underlay. Obviously budget is sometimes an issue with underlays, but it is well worth the extra money. Without underlay, there would be the following financial drawbacks:

  • Wear. The spongy, stretchy nature of underlay means it offers a level of ‘give’ which helps to absorb impact, preventing the back of the carpet from rubbing against the floorboards and wearing out. Skipping the underlay is likely to mean you’ll need to buy a new carpet much sooner.
  • Heating bills. Without underlay, your room is much less insulated, which increases your heating bills.

9. How much does carpet underlay cost? 

Some underlay can be as cheap as £2.50 a square metre. But beware, cheap underlay can easily disintegrate, leaving an uneven carpet with worn backing and little ‘give’. All of the underlay available from United Carpets & Beds comes with a special Textron layer which:

  • offers excellent ‘bounce’
  • has a clean appearance
  • reduces carpet rucking
  • is easy to install

The table below shows the prices and thickness of underlay on offer at United Carpets & Beds:




Cost (per m2)

Airstep Super Underlay

8 mm


Airstep Deluxe Underlay

10 mm


Airstep Elite Underlay

12 mm


Airstep Diamond Underlay

12 mm


Airstep Emerald Underlay

10 mm


10. Can carpet underlay be used for laminate flooring?

No, carpet underlay is too thick and bouncy. The amount of springing movement it allows could prevent the laminate from locking together properly.

For laminate flooring you will require special laminate underlay, which is considerably thinner. Woodtex Laminate Underlay has a high density to reduce noise levels while also incorporating a moisture barrier that eliminates the need for extra moisture protection.

11. How thick should carpet underlay be?

Underlay is generally available in thicknesses ranging from 8 mm–12 mm:





8 mm–9 mm

Often cheaper than thicker underlays. Hardwearing but unlikely to offer the luxuriousness associated with thicker underlay. Not suitable for carpet being laid on concrete floors.


10 mm–11 mm

A good all-round choice for underlay throughout the home, including high-traffic areas such as stairs.


12 mm

The most luxurious choice. Likely to be expensive but will give carpet an ultra-comfortable bounce underfoot. Ideal for maximum comfort in bedrooms and lounges.

As underlay acts as a protective cushion for your carpet, any underlay that is less than 8 mm may reduce the life of your carpet and make it less comfortable to walk on.

It’s also important to consider footfall. Very thick underlay does create a soft and luxurious feel but also allows for a lot of movement. Placing thick underlay in a busy area—such as a hallway or on stairs—may damage both the underlay and the carpet.

12. How can I ensure the underlay won’t cause my doors to drag?

If you’re replacing a particularly worn out carpet or fitting carpet for the first time (for example, if you’re replacing laminate flooring), the height of the carpet may interfere with the movement of your doors.

If you think your doors will drag on the carpet, you may need to take some length off the bottom of them.

You can do this in five simple steps:

  1. Remove the doors.
  2. Fit the underlay and carpet.
  3. Measure the distance from the carpet to the bottom of the door hinge rebate on the door frame. The rebate is the indent in the door frame that the hinges fit into.
  4. Measure the distance from the bottom of the door to the bottom of the hinge on the door.
  5. Subtract this from the measurement worked out in point 3 and that is how much you need to take off the bottom of the door.

Alternatively, you can simply the plain the amount of space required off the bottom of the door. Some stores offer this as an additional service

Find out more information about buying and fitting new carpets by visiting our guide: A step-by-step guide to choosing, buying and fitting a new carpet

13. What underlay density should I choose?

Underlay thickness is not the only thing to consider. Density also plays a part and can affect how comfortable a carpet feels. For example, an 11 mm thick piece of dense underlay may feel firmer and less luxurious than a 9 mm piece of less dense underlay.

Although denser underlay may not necessarily be the most comfortable underfoot, it’s often the best choice for high-traffic areas such as hallways and stairs to ensure carpet lasts as long as possible.

Best underlay for optimum density: Airstep Deluxe underlay

Airstep Deluxe underlay

Thickness: 10 mm

PRICE: £11.99 m²

Buy this underlay now

14. What’s the best choice for thick underlay?

The 12 mm thick Airstep Diamond underlay will maximise the life of your carpet, even in high-traffic areas, and make it feel thicker and softer for longer.

15. Which way up does carpet underlay go?

If your underlay has a sticky or shiny surface, that should be in contact with the floor. If there is no shiny surface, one side usually has more of an even surface which is made from a thin backing material. This should be face up, so it’s in contact with the carpet. Hence, the spongy material that makes up most of the underlay should be face down, in contact with the floor.

All underlay from United Carpets and Beds features a United Carpets and Beds logo on the side that should be face up.

16. How long does carpet underlay last?

Underlay is excellent for all the above reasons, but its effectiveness does start to diminish from the moment it’s used. Therefore, unless you have had a change of heart and replaced your carpet only after a few months of fitting it, you should lay new underlay every time you lay new carpet.

Need a hand fitting your underlay?

United Carpets & Beds offers free fitting when you buy the same amount of Airstep or Treadmore underlay as carpet.

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