Do I Really Need New Underlay? (The Truth)

Quick answer: No — reusing old underlay almost always shortens the life of new carpet and can void the manufacturer's warranty. Underlay compresses over time and stops cushioning and insulating properly, so putting new carpet on old, flattened underlay crushes the pile against the hard floor beneath it.

Why we get asked this every week

It's the most common question on a home visit: 'Can we just use the old underlay?' The honest answer is almost always no, and here is why it matters more than people expect.

Underlay is the shock absorber, not padding

Underlay acts as the shock absorber for your carpet. Every time you step, it compresses and springs back. Over roughly 10 years of normal use, it loses that bounce and becomes a flat, dead layer of foam or rubber that can no longer protect the carpet backing above it.

What happens if you skip new underlay

If you fit new carpet on old, flat underlay, the pile gets crushed against the hard floor with every footstep. This can cut the lifespan of an otherwise good carpet by up to 50%, and most carpet manufacturers will void the product warranty if it's fitted on underlay that doesn't meet their spec. It's a false saving — you end up replacing the carpet sooner, not later.

Types of underlay we use

• PU Foam (Cloud 9, Tredaire and similar): The modern standard. Lightweight, good thermal insulation (higher tog rating), and comfortable underfoot. Best suited to bedrooms and lounges where softness matters.

• Rubber Waffle: The traditional choice. Durable in the short term but can degrade into a crumbly dust over time, especially under heavy furniture.

• Crumb Rubber / High-density: Firm and flat rather than soft. This is what we recommend for stairs and areas with heavy furniture, since it resists 'walking' and indentation far better than a soft foam grade — see our best carpet for stairs guide for why stairs need a different spec entirely.

Tog ratings and where they matter

Tog rating measures thermal insulation, not comfort or durability. A higher tog underlay keeps a room warmer — useful over cold concrete ground floors — but a very high tog can sometimes be too soft and springy for stairs or areas with heavy furniture. We'll recommend the right balance for each room during your measure.

Underlay for natural flooring is different

Sisal, seagrass, coir and jute don't use standard PU foam underlay. They're typically fitted using a 'double-stick' method with a specialist underlay bonded to the subfloor, because the natural fibre needs a firm, stable base rather than a cushioned one. See natural flooring maintenance and our sisal pros and cons guide.

Signs your existing underlay needs replacing

If the floor feels noticeably softer or lumpier underfoot than it used to, if you can see indentation marks that don't spring back, or if the carpet above it already shows premature wear, the underlay is usually the culprit rather than the carpet itself.

What it costs

Underlay typically adds a modest amount per square metre on top of the carpet price — usually a small fraction of the total job. It's one of the cheapest ways to extend the life of an expensive carpet, and it's included as standard in our supply and fit quotes. See the full cost guide for how it fits into an overall quote.

The mattress analogy

Think of underlay as the mattress and carpet as the sheet. You wouldn't put a crisp new sheet on a lumpy, collapsed mattress and expect a good night's sleep. Invest in the right underlay for each room and the carpet above it will look better, feel better and last longer.

Book a measure

On a free home visit we'll check your existing underlay and recommend the right grade for each room — no guesswork. We fit across West Sussex including Bognor Regis, Chichester and Worthing.