A tog rating tells you how strongly a duvet resists heat flow, which makes it a practical way to compare duvet warmth. Higher tog ratings generally mean more insulation, while lower ratings mean less. Tog is not the same as duvet weight, thickness, GSM, breathability, or overall quality, so the number should be considered alongside your room, sleep preferences, filling, and duvet construction.
Quick Answer
Tog measures a duvet’s thermal resistance—how strongly it resists heat flow. A higher tog usually feels warmer, while a lower tog usually feels cooler. It does not measure weight, thickness, breathability, or quality. Choose tog based on room warmth, season, personal preference, and the duvet’s filling and construction.
Key Takeaways
- Tog measures thermal resistance, so it is primarily a guide to how insulating a duvet is.
- Lower tog ratings are generally suited to warmer conditions; higher ratings provide more insulation for cooler conditions.
- Duvets commonly sit somewhere around 1 to 15 tog, although available ratings and seasonal recommendations vary by manufacturer.
- A low-tog duvet is commonly chosen for summer, a mid-tog duvet for milder or transitional weather, and a higher-tog duvet for winter.
- Tog does not tell you how heavy, breathable, soft, or durable a duvet will feel. Filling, casing, loft, construction, and personal preference still matter.
What Does Tog Mean in Bedding?
Tog is a unit used to express thermal resistance. In practical bedding terms, it tells you how strongly a duvet resists heat passing through it. The higher the thermal resistance, the more effectively the duvet insulates you from the cooler air around you.
The original tog unit was developed for textiles as a more convenient way to express thermal resistance. One tog equals 0.1 m²·K/W. The original work by F. T. Peirce and W. H. Rees was published in the Journal of the Textile Institute.
For shoppers, you do not need to calculate thermal resistance yourself. Use the stated tog rating to compare insulation. A low rating is usually better for warm weather or people who easily overheat, while a higher rating is more useful when the room is cool or you prefer a warmer bed.
For example, a duvet around 3 to 4.5 tog is commonly sold for warmer conditions, mid-range products such as 7 to 10.5 tog offer more insulation, and products around 12 to 15 tog are commonly marketed for colder weather. These are shopping guidelines rather than universal comfort rules.
How the Tog Scale Measures Warmth
The tog scale describes thermal resistance rather than temperature itself. A 15-tog duvet does not heat itself to a particular temperature; it simply provides more resistance to heat flow than a low-tog duvet under comparable test conditions.
One tog equals 0.1 m²·K/W, so a higher number represents greater thermal resistance. Consumer duvets are commonly sold across a range of roughly 1 to 15 tog, although individual manufacturers may offer ratings outside the most familiar seasonal bands.
That makes tog useful for comparing duvet insulation without guessing from thickness or weight. However, it is still only one specification. How warm you feel in bed also depends on your bedroom temperature, sleepwear, mattress, duvet coverage, filling, humidity, and individual thermal comfort.
Tog measures thermal resistance. It does not measure duvet weight, breathability, softness, or overall quality.
Why Tog Is Different From Duvet Weight
You should treat tog as a measure of thermal resistance, not physical weight. A high-tog duvet can be relatively light if its filling traps air efficiently, while a heavier duvet can have a lower tog if its materials or construction transfer heat more readily.
Filling type, fill amount, loft, casing, and construction all influence the result. Research on bedding systems shows that both the material and the amount of filling can change thermal insulation, so weight alone is not enough to predict warmth.
Tog Measures Warmth, Not Weight
A duvet’s weight may affect how it feels on your body, but it does not tell you its thermal resistance. That is what the tog rating is designed to communicate.
Two duvets can therefore weigh about the same yet have different tog ratings. Likewise, two duvets with the same tog can have noticeably different weights, drape, softness, and bulk.
When warmth is your main concern, compare tog first. Then compare weight and filling according to whether you prefer a light, lofty duvet or a heavier, more substantial feel.
Fill Material Affects Insulation
Fill material changes how a duvet creates and holds insulating air spaces. That is one reason two duvets with similar dimensions or fill weights can perform differently.
- Down can provide high thermal insulation for its weight because its structure creates substantial loft and traps still air.
- Wool has different moisture-handling and temperature-regulating characteristics and can feel different from down even at a similar warmth level.
- Synthetic fillings vary widely. Hollowfibre, microfibre, recycled polyester, and other engineered fills should be judged by the finished duvet’s tog and construction rather than by fibre type alone.
A 10.5-tog down duvet, for example, may feel lighter and less bulky than some synthetic 10.5-tog products even though their stated thermal resistance is similar.
What Tog Does Not Measure
Tog answers one main question: how much thermal resistance does the duvet provide? It does not directly measure several other qualities that affect comfort.
- Weight: a high-tog duvet does not have to be heavy.
- Thickness: visible thickness is not a reliable substitute for a tested insulation value.
- Breathability: airflow and moisture movement depend on the filling, casing, and construction.
- Softness and drape: two equal-tog duvets may feel completely different against your body.
- Durability: a higher tog does not mean better materials or longer life.
- GSM: grams per square metre describes material weight per area, not thermal resistance.
Note: Use GSM mainly when comparing similar products made with the same type of filling and construction. A 350gsm duvet made from one filling is not automatically warmer than a 200gsm duvet made from another. Tog is the more useful specification when your main goal is comparing thermal resistance.
Common Tog Ratings for Summer and Winter
Tog ratings are often grouped into seasonal categories, but the boundaries vary between brands. Current consumer guidance generally places lightweight summer duvets at the lower end of the scale and winter duvets at the higher end.
| Approximate Tog Range | Common Use | Typical Feel |
|---|---|---|
| 1-4.5 | Summer / warm rooms | Light insulation |
| 7-10.5 | Milder weather / spring and autumn | Moderate warmth |
| 12-15 | Winter / cooler rooms | Higher insulation |
These bands are best treated as starting points. For example, Silentnight’s current guidance describes 4.5 to 7.5 tog as suitable for summer, 10.5 tog as an all-season option, and 13.5 to 15 tog as winter ratings. Other manufacturers use slightly different categories.
If you want one duvet system to cover several seasons, an all-season set can be useful. A common arrangement combines a lighter 4.5-tog layer with a 9-tog layer to create a warmer 13.5-tog configuration when the two are attached.
What Tog Fits Your Room Temperature?
Your bedroom temperature matters, but there is no universal adult room-temperature-to-tog chart. Research on sleep thermal comfort shows that ambient temperature and bedding insulation work together, while duvet coverage and individual differences also change how warm a sleeper feels.
A practical way to choose is to think in broad categories:
- Warm bedroom: start toward the lower end of the tog scale, especially if you sleep hot.
- Moderate bedroom: a mid-range tog often provides a useful balance between insulation and flexibility.
- Cool bedroom: move toward a higher tog if you regularly feel cold and do not want to rely on extra blankets.
Rooms around 20°C/68°F or warmer will often call for less insulation than cool rooms around 16°C/61°F, but those temperatures should not be treated as automatic cutoffs. Your sleepwear, mattress, duvet cover, whether you share the bed, and your own thermal preference can all shift the comfortable choice.
A 2023 study in the Journal of Thermal Biology found that duvet thermal resistance and ambient temperature both influence sleep thermal comfort, reinforcing why a single temperature-to-tog formula cannot fit everyone.
Warning: These adult duvet recommendations should not be applied to babies. The NHS says pillows and duvets are not safe for babies under one year because of suffocation and overheating risks. Use age-appropriate sleepwear or a properly fitted baby sleeping bag and follow NHS safer-sleep guidance and the product manufacturer’s instructions.
Which Tog Suits Your Sleep Style?
Your sleep style should guide tog selection as much as the season because two people can feel very different under the same duvet.
If you tend to be a hot sleeper, start with a lower tog. A lightweight duvet in the 1 to 4.5 range is a common choice for summer and may also work for people who sleep warm in heated homes.
If you regularly sleep hot, start with a lower tog and increase insulation only if you actually feel cold.
If you tend to sleep cold, a higher tog such as 12 to 15 may be more comfortable during cold weather. In milder conditions, 7 to 10.5 tog can offer moderate insulation without committing to a full winter duvet.
Couples can be harder to match because one person may sleep much warmer than the other. In that situation, separate duvets or split-tog products can give each sleeper a different insulation level.
Hormonal changes, medications, illness, and other body changes can also affect how warm you feel at night. If new or persistent night sweats are a concern, changing the duvet may improve comfort but should not be treated as a substitute for appropriate medical advice.
A natural filling such as wool or down may feel different from a synthetic fill even at the same tog, so consider weight, drape, moisture handling, and care requirements as well as the number on the label.
How Filling Affects Duvet Warmth
Your duvet’s filling type affects its insulation, loft, weight, moisture handling, and feel. Different materials create different structures for trapping air, so filling quality and construction matter alongside the stated tog.
A 2026 Building and Environment study examining polyester, cotton, down, and mixed fillings found that filling material and areal weight both affected bedding insulation. Under comparable weight conditions, down produced the highest insulation among the fillings tested.
Distribution also matters. Quilting, baffles, stitching, and fill migration can create warmer and cooler areas, which is why two duvets with similar fill materials do not necessarily perform identically.
Filling Type Matters
Different fillings create different combinations of warmth, weight, loft, breathability, moisture handling, and care needs.
- Down: known for a high warmth-to-weight ratio and substantial loft when high-quality fill is used.
- Wool: offers insulation with distinctive moisture-management and temperature-regulating characteristics.
- Synthetic fibre: available in many constructions, including hollowfibre and microfibre, with performance varying widely between products.
Do not assume that “natural” automatically means warmer or that “synthetic” automatically means cooler. Compare the finished duvet’s tog, weight, casing, construction, and care requirements.
Loft And Insulation
Loft describes how much volume and trapped air a filling creates. Trapped still air can contribute strongly to insulation, which is why fluffy, resilient filling structures can provide substantial warmth without necessarily feeling extremely heavy.
When comparing duvets, consider loft, tog rating, and filling type together. Construction also matters because compressed sections and quilting seams can create different heat-transfer paths through the duvet.
GSM can still be useful within a closely matched product range. For example, a manufacturer may use a lower-GSM version of the same synthetic filling for a summer duvet and a higher-GSM version for a colder-weather model. That does not mean a 350gsm duvet of one material is automatically warmer than a 200gsm duvet made with a different filling.
If you want warmth without excessive bulk, look for an efficient filling and construction rather than choosing by weight alone.
Natural Vs Synthetic
Natural and synthetic fillings can both produce warm, comfortable duvets. The important differences are usually in weight, loft, moisture handling, washability, allergy considerations, price, and feel rather than a simple natural-versus-synthetic warmth ranking.
- Down can provide high insulation at relatively low weight because of its loft.
- Wool offers warmth while also handling moisture differently from down and many synthetic fibres.
- Synthetic materials can be engineered for different warmth levels and may offer practical benefits such as easier washing, but breathability varies by product.
If you want a light, lofty feel, some down products may suit you. If easy care is more important, a synthetic duvet may be more practical. If you prefer the characteristics of wool, compare its stated warmth and care requirements rather than judging it only by fill weight.
In every case, the filling shapes the duvet’s weight and feel, while the tog rating remains the more direct guide to thermal resistance.
How Combined Tog Duvets Work
Combined or all-season duvets use two separate layers that can be used independently or attached together, giving you several warmth options from one set.
A common arrangement pairs a 4.5-tog duvet with a 9-tog duvet. You can use the lighter layer in warmer weather, the 9-tog layer during milder or transitional conditions, and attach them to create a manufacturer-rated 13.5-tog winter configuration.
Manufacturers commonly use poppers, clips, ties, or other fasteners to keep the two layers aligned.
This design can be convenient if your bedroom changes substantially across the year because you can adjust the insulation without storing several full-size duvets.
Do not assume that every pair of layers can simply be added together or that a combined duvet will provide an extra margin above the stated figure. Check the manufacturer’s individual and combined tog ratings for the exact product.
Pro Tip: If your room changes a lot between summer and winter, an all-season set can be more flexible than choosing one very high or very low tog for the entire year.
How Tog Ratings Are Tested
Tog ratings are based on measurements of thermal resistance under controlled conditions. Laboratory methods measure the relationship between temperature difference and heat flow through a textile sample so insulation can be expressed consistently.
The tog system has historical links to the Shirley Institute and the Shirley Togmeter, a guarded-hotplate-style approach used in textile testing. Older references often cite British Standard BS 4745.
That older standard should not be presented as a current “BS 4745:2005” standard. The British Standards Institution lists BS 4745:1990 as withdrawn on November 25, 2005.
For current standards context, BSI lists BS EN ISO 11092:2026 as a current standard for measuring thermal and water-vapour resistance under steady-state conditions. Its scope includes multilayer assemblies used in products such as clothing, quilts, sleeping bags, and upholstery.
In simple terms, the laboratory controls the test conditions and measures how readily heat passes through the sample. Greater resistance to that heat flow means a higher insulation value.
- Condition and position the textile sample according to the relevant test method.
- Establish controlled temperatures and heat flow across the specimen.
- Measure the sample’s thermal resistance.
- Express the insulation result using the applicable measurement system, which may include the familiar tog value for consumer bedding.
Testing gives you a useful basis for comparing thermal resistance, but it cannot perfectly predict how every person will feel in a real bedroom. Your duvet cover, sleepwear, mattress, body coverage, room conditions, and personal physiology still affect comfort.
Frequently Asked Questions
Is a 7.5 Tog Duvet Too Warm for Summer?
It can be, especially in a warm bedroom or if you tend to sleep hot, but 7.5 tog is not automatically too warm for everyone. Summer recommendations vary between brands, and some place 7.5 tog near the upper end of their summer range. If overheating is common for you, a lower tog such as 1 to 4.5 is a safer starting point.
Is a 10.5 Tog Duvet Warm Enough for Winter?
For some people, yes. A 10.5-tog duvet can work in a heated or mild bedroom, particularly if you sleep warm. If your room is consistently cool or you feel cold easily, a higher winter rating such as 12 to 15 tog may provide more insulation.
Is a 9 Tog Duvet Warm Enough for Winter?
A 9-tog duvet provides moderate insulation and may work in a mild, heated bedroom or for someone who sleeps warm. In colder rooms, it will generally provide less insulation than a 12, 13.5, or 15-tog winter duvet.
Is 4.5 Tog Too Hot for Summer?
Not necessarily. A 4.5-tog duvet is commonly sold as a summer option and can suit people who want light insulation without sleeping under only a sheet. If your bedroom becomes very warm or you regularly overheat, an even lower tog may feel better.
Does Tog Measure Duvet Weight?
No. Tog measures thermal resistance, while duvet weight is the physical mass of the finished product. Two duvets can have the same tog rating but very different weights because their fillings, casings, loft, and construction differ.
Do All-Season Duvet Tog Ratings Add Together?
Many all-season sets are specifically designed that way—for example, a manufacturer may rate a 4.5-tog layer and a 9-tog layer as 13.5 tog when attached. Use the combined rating stated by the manufacturer rather than assuming that any two separate duvets can be added mathematically.
Conclusion
So, what does tog mean for your bedding choice? It is a measure of thermal resistance that helps you compare how insulating duvets are. Lower ratings generally suit warmer conditions, while higher ratings provide more insulation for colder rooms and seasons.
Use tog as your starting point, then consider your bedroom temperature, whether you sleep hot or cold, duvet filling, weight, loft, casing, and construction. Two duvets with the same tog can still feel very different, so the best choice is the one that combines the right insulation level with the weight and feel you prefer.
Sources
- Peirce & Rees, Journal of the Textile Institute — The Transmission of Heat Through Textile Fabrics, Part II — historical development and definition of the tog unit.
- British Standards Institution — BS EN ISO 11092:2026 — current steady-state thermal and water-vapour resistance testing standard covering quilts and similar textile assemblies.
- British Standards Institution — BS 4745:1990 — confirms the older textile thermal-resistance standard was withdrawn in 2005.
- Building and Environment, 2026 — Measurement and prediction of bedding insulation — evidence on filling material, filling weight, coverage, and bedding thermal insulation.
- Journal of Thermal Biology, 2023 — Effect of quilt thermal resistance on sleep thermal comfort — evidence that ambient temperature and duvet insulation jointly influence thermal comfort.
- NHS — Safer sleep advice for babies — infant sleeping-bag tog guidance and safer bedding recommendations.
