Most “thermal curtains” sold in the UK aren’t doing what the label suggests. They’re mid-weight curtains with a marketing sticker and a price tag inflated by about 40%. Some genuinely reduce heat loss; many don’t. The same is true of draught excluders — some interventions cut heating bills measurably, others are decorative.
This guide is a take-no-prisoners look at what actually keeps heat in a UK home and what’s wishful thinking. By the end you’ll know which products to buy, which to skip, and the order to spend in if your budget is small. The honest answer for most readers is that draught-proofing your doors first will give you a bigger return than upgrading your curtains.
What thermal curtains actually do (and don’t)
A curtain doesn’t insulate a window. It creates a buffer of still air between the cold glass and the warm room, and it slightly reduces radiant heat loss from the room into the cold pane. That’s it. The thicker the curtain (and the less air can flow around it), the bigger the buffer.
There are three things that drive thermal performance, and they matter in this order:
- Lining weight and material. A heavy interlined curtain — meaning a separate insulating layer between the face fabric and the lining — outperforms a single-layer “thermal” curtain by a wide margin. Lining weight is measured in grams per square metre (gsm); look for 200gsm+ if you want meaningful insulation.
- Fit. A thermal curtain that doesn’t touch the floor, doesn’t overlap the wall on either side, and has a gap above the rail is a heat-loss chimney. Cold air drops behind the curtain, warm air rises above it, and you’ve created a convection loop that bypasses the curtain entirely.
- Closing them. Open thermal curtains do nothing. This sounds obvious; in practice many UK households leave living-room curtains half-drawn through the evening because of the layout of the sofa.
Get those three right and a good thermal curtain reduces window heat loss by 15–25%. Get any of them wrong and the figure collapses. A “thermal blackout curtain” hung from a too-short rail with daylight visible at the top is barely better than a normal curtain.
What to look for when buying
Skip the marketing claims and look for these specifics:
- Lining weight quoted in gsm. If the listing doesn’t state it, assume it’s low. 200gsm+ is the floor for genuine thermal performance; 280–340gsm is where the noticeable winter difference is.
- Triple-weave or three-layer construction. Means a face fabric, a black-out layer, and a thermal layer. Single-weave “thermal” curtains are mostly marketing.
- Curtain length. Buy long enough to puddle on the floor by 2–4cm. Curtains stopping at the radiator are wasting their thermal performance — they trap warm air against the cold glass instead of holding it in the room.
- Width. The curtain pair should be at least 1.5x the rail width when closed (2x is better) and overlap the wall by 15cm either side of the window opening.
- Heading style. Pencil pleat and eyelet headings allow more airflow over the top of the curtain than pinch pleats with a pelmet. If you can fit a pelmet, you’ll get noticeably more thermal performance.
Comparison: which type does what
| Type | Real-world thermal performance | When it makes sense | When to skip it |
|---|---|---|---|
| Triple-weave thermal blackout curtains | Good (15–25% window heat loss reduction with proper fit) | Bedrooms, north-facing rooms, single-glazed flats | Already have heavy lined curtains |
| Mid-weight “thermal” curtains | Modest (5–10%) | Better than thin curtains; budget option | If you can stretch to a triple-weave version |
| Standalone thermal curtain linings | Good (adds 10–20% to existing curtains) | When you love your existing curtains and don’t want to replace them | When the curtains themselves are very lightweight |
| Window film (insulating shrink kit) | Modest to good (8–15%) | Single-glazed sash windows, conservatories, listed buildings | Modern double-glazed windows in good condition |
| Secondary glazing (DIY perspex) | Strong (25–40%) | Cold rooms with old windows, Victorian flats | Rented properties where you can’t make holes |
The honest hierarchy: if your curtains are already heavy and lined, your money goes further on draught-proofing or window film than on new curtains. If your curtains are lightweight or you’re in a single-glazed property, upgrading to a triple-weave thermal blackout pair is the single biggest curtain-side intervention available.
View Yorkshire Linen Triple Weave Thermal Blackout Curtains options on Amazon
Check Yorkshire Linen Thermal Curtain Lining price on Amazon
Compare current Amazon options for the lining weight quoted in gsm before buying — that’s the spec that actually predicts winter performance.
Draught excluders for doors: where the easy wins are
If you can only spend £20 this winter, spend it on door draught-proofing, not curtains. The reason: a typical UK internal door has 4–8mm of gap at the bottom and a similar amount around the frame. That’s a continuous opening to a cooler space, often a hallway or staircase that connects to the front door. A 6mm gap along a standard 760mm door is the same as leaving a window ajar on a credit-card-sized opening — for the entire winter.
Front doors are worse. Older front doors leak around the threshold, the letterbox, the keyhole, and along the frame. Each of these is fixable for under £10.
What works:
- Brush-strip excluders for the bottom of internal doors. Self-adhesive or screw-fixed; the screw-fixed versions last longer and don’t drop off in summer.
- Threshold strips for the bottom of front doors. Aluminium strip with a rubber blade that seals against the floor.
- Letterbox brushes and flaps. A two-stage brush-and-flap fitting cuts letterbox draught by 80%+.
- Keyhole covers. Pennies, but a Yale keyhole leaks surprisingly badly without one.
- Self-adhesive foam strip around door frames. Cheapest of the lot. Lasts 3–5 years.
See Stormguard Brush Door Strip on Amazon
Compare Exitex Threshold Strip options on Amazon
What to skip: the long fabric “snake” draught excluders sold in homewares shops. They look the part and they do help slightly, but they fall over, they slide out of position when the door opens, and a £4 brush strip outperforms them every winter for the next decade.
Window draught-proofing: the second tier
Older sash and casement windows leak air around the frames. Modern double-glazed windows in good condition mostly don’t. Before buying anything, run your hand along the inside of the window frame on a windy day; if you feel air movement, draught strip is worth fitting.
What works on older windows:
- V-strip (P-strip) self-adhesive seal for the meeting rails on sash windows
- Compression-seal foam strip for casement windows that close against a frame
- Silicone sealant for fixed gaps around the frame perimeter
- Insulating window film kits (the shrink-fit plastic with a hairdryer) for single-glazed windows in unheated rooms
Window film looks ugly and feels like a student fix, but on a single-glazed kitchen or bathroom window it can knock 10–15% off the room’s heat loss for under £10. In a rented flat where you can’t replace the windows, it’s the best per-pound intervention available.
Where this fits in a wider winter setup
Heat retention is one component of a larger winter-comfort system. The two it pairs with most directly:
- A drying setup that doesn’t fight the heat retention. No point sealing the doors and then opening every window for two hours because the laundry’s gone damp. Our winter laundry setup for small UK homes covers the integrated approach.
- Smart heating controls. Once your heat retention is solid, smart thermostats and smart radiator valves stop wasting heat in unused rooms — see smart radiator valves vs smart thermostat.
There’s also a third layer worth flagging if you’re doing all of this systematically: an energy-bill-killer winter setup that maps which combinations give the biggest return per pound spent.
Your buyer’s checklist
Before you order, walk through these:
- Have you actually felt for draughts? Hand on doorframe, hand on window frame, on a windy evening. Find the leaks before you buy seals.
- Are your existing curtains lightweight or heavy? Heavy and lined → buy linings or seals instead. Lightweight → upgrade the curtains.
- Do your curtains touch the floor? If they stop above the radiator, you’re heating the back of the curtain and the window, not the room.
- Do they overlap the wall by 15cm either side? If not, replace the rail with a wider one before replacing the curtains.
- Have you draught-proofed the front door’s letterbox and keyhole? These two interventions cost under £15 combined and pay back within a single billing cycle.
- Are there single-glazed windows in unheated rooms? Window film for those rooms first; better curtains second.
- Do you rent? Brush strips, P-strip seals, and window film all come off without damage. Curtain rails are a grey area; check your lease.
Common mistakes
Buying “thermal” curtains without checking the lining weight. A 90gsm “thermal” curtain is a thin curtain. Look for 200gsm+ minimum.
Hanging good curtains on a too-short rail. The rail should extend at least 15cm beyond the window on each side. Otherwise the curtain bunches against the wall and creates the cold-air bypass described above.
Sealing draughts without ventilation. A well-sealed home needs deliberate ventilation — trickle vents, a brief daily window open, or an extractor fan. Otherwise humidity climbs and you swap a heat-loss problem for a damp problem.
Putting curtains in front of radiators. The radiator heats the curtain and the window, not the room. If you can’t move the curtains, move the radiator (longer term) or fit reflective foil behind the radiator (cheap, immediate).
Spending big on curtains when the front door is the actual problem. Most UK households lose more heat through under-sealed doors than through windows. Diagnose first, spend second.
FAQ
Do thermal curtains work in summer too? Yes — they reduce solar gain and keep rooms cooler in heat waves. The same triple-weave construction that traps warm air in winter blocks radiant heat in summer.
Do I need blackout if I just want thermal? Most triple-weave thermal curtains are also blackout because the construction is the same. You can buy thermal-only curtains, but they’re a smaller market and rarely cheaper.
What’s the difference between thermal curtains and thermal blinds? Blinds (Roman, roller, or honeycomb cellular) sit closer to the glass and can be effective, especially honeycomb cellular blinds. They generally outperform curtains on a strict thermal basis but lose to curtains on side-overlap and bottom-puddle, which makes the practical difference smaller than the spec suggests. Use them together for the strongest result.
Will draught-proofing make my house too humid? Possibly, if you over-seal without ventilation. Keep trickle vents open, run extractor fans during cooking and showering, and consider a humidity monitor to track levels. Anything sustained above 60% RH means you need more ventilation.
Is window film worth it for double-glazed windows? Usually not. Modern double glazing is already much better insulated than a film can achieve. Film is for single glazing, leaky old windows, and conservatories.
Can I fit thermal linings to existing curtains? Yes — clip-in linings hook onto the existing curtain rings. They add roughly 10–20% improvement without replacing the curtains, and they’re the cheapest serious upgrade if you like your current ones.
The takeaway
If you’ve got £30 to spend on heat retention this winter, spend it on door draught-proofing — letterbox, keyhole, brush strip, threshold seal. If you’ve got £100, add a P-strip seal kit for old windows and a packet of self-adhesive foam for door frames. If you’ve got £200+, then look at thermal curtains or thermal linings for the rooms you spend the most time in.
The order matters. Most UK households buy the curtains first, find the heating bill barely moves, and conclude that thermal curtains don’t work. They do work — but they work alongside good draught-proofing, not instead of it. Get the cheap interventions in first; the curtains will earn their money once they’re not fighting a continuously open letterbox.
Compare current Amazon options for any of the products above and look at the spec rather than the marketing — gsm for linings, brush length for door strips, and seal width for window kits.