13.5 Tog vs 15 Tog Duvet: Is Ultra-Warm Worth It?

Jul 17, 2026 / Oct 5, 2026 · 6 min read · togs bedding uk ·

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The standard winter duvet, and the step above it

A few weeks into winter, with the heating off overnight, a 13.5 tog duvet can start to feel thin, and the 15 tog on the shelf above it looks tempting. On paper the step is small: 1.5 tog, about 11% more thermal resistance. In practice the question is whether your bedroom is cold enough to need it, and whether the labels are precise enough for the gap to matter.

UK retailers agree on where the two sit. Primark's tog guide calls 13.5 tog "the best duvet for staving off chills in winter." Marks & Spencer says "a 13.5 duvet is one of the warmest options." The testing laboratory IDFL gives the British Standard range as running "from 4.5 (summer weight duvet) to 15.0 (suitable for very cold winters)", and says 13.5 tog "is the most commonly used tog in Ireland and the UK."

So 13.5 tog is the normal winter weight, and 15 tog is for very cold rooms or very cold sleepers.

What one tog step means

A tog measures how well a fabric resists the flow of heat. According to Wikipedia's article on the unit, one tog equals 0.1 square metre kelvin per watt, and the test behind it is set out in the British Standard BS 4745. Wikipedia also notes that British duvets are sold in steps of 1.5 tog, from 3.0 tog for summer up to 16.5 tog for extra-warm. So 13.5 and 15 tog are neighbours on the same ladder, one step apart.

Our explainer on how tog ratings are measured covers the test in detail.

How far to trust the gap

This is the part most comparisons miss. Wikipedia says the values printed on British duvets "are a minimum; actual values may be up to 3 tog higher." Bensons for Beds says the same: the stated rating "is generally a minimum, meaning that the duvet inside could, in fact, have a rating of up to three togs higher."

That margin is twice the gap between the two ratings. A duvet labelled 13.5 tog could, in principle, be as warm as one labelled 15 tog, or warmer. Two duvets from different makers with these labels are not guaranteed to be 1.5 tog apart.

IDFL adds two more limits. Ratings are measured on "a new quilt on a flat surface", and "poor quality quilts lose their tog ratings fast, particularly if they're washed." Its conclusion is that a tog rating "is at best only a rough guide to how warm you'll be."

The practical lesson: compare the two ratings within one brand's range, where the same maker is applying the same method, rather than across brands.

How easy each is to buy

13.5 tog is far easier to find. When we checked Dunelm's duvet range on 5 October 2026, it listed 27 duvets at 13.5 tog and 5 at 15 tog. Only 10.5 tog had more choice, with 40.

Many 13.5 tog duvets are sold as two-piece sets. Marks & Spencer's All Seasons duvet is "a 3-in-1 combination of our 4.5 and 9 tog duvets", and Wikipedia describes the same pairing: a 4.5 tog and a 9.0 tog duvet that join with press studs or Velcro "to become a 13.5 tog winter duvet." If you want winter warmth without a single heavy duvet the rest of the year, a set like this is the usual answer. There is no equally common two-piece route to 15 tog.

Who needs 13.5 tog

The retailers' seasonal guides put 13.5 tog inside the winter band:

Argos: winter is 12 to 15 tog, for "cold sleepers, cooler bedrooms."
Marks & Spencer: 12 to 15 tog is "Great for winter and cold nights."
Wikipedia's comfort bands: winter is 12.0 to 13.5 tog.
Silentnight: 10.5 to 13.5 tog "is ideal for autumn and winter", and if you tend to get night sweats, "you'd be better off with a low tog."

Notice that only Argos and Marks & Spencer stretch their winter band to 15 tog. Wikipedia and Silentnight stop at 13.5.

Bensons says that for most Brits, a duvet of "somewhere between 10.5 and 13.5 tog is the go-to, providing a good level of warmth in our typically cool climate." IDFL notes that 12.0 and 10.5 tog duvets "are becoming more popular" as more homes have central heating. If your bedroom is heated through the night, 13.5 tog is likely to be enough, and possibly more than enough.

Who might need 15 tog

The sources describe 15 tog in similar terms: IDFL's "suitable for very cold winters", Argos's "cold sleepers, cooler bedrooms" at the top of its winter band, and Primark's list of winter ratings that includes "12, 13.5 and 15". Taken together, 15 tog makes sense if:

your bedroom stays cold overnight because it is unheated or the heating is off,
you already use a 13.5 tog duvet and still feel cold on most winter nights, or
you are buying for a cold guest room that is rarely heated.

It makes less sense in a centrally heated home or for a warm sleeper. Bensons warns that even a 13.5 tog duvet "can be difficult to live with in the height of summer," so a 15 tog duvet is a winter-only purchase.

Weight and filling

A higher tog does not have to mean a heavier duvet. Primark explains that "synthetic fillings often require more material to match the insulation of a down duvet," which "results in heavier duvets with the same tog rating as lighter, natural-filled ones." Argos adds that tog ratings do not relate to weight, which "tends to be determined by the filling inside."

If you want 15 tog warmth without much weight, a natural-filled duvet is the likelier route. If price matters more, a synthetic 15 tog will cost less but will be bulkier.

Side by side

	13.5 tog	15 tog
Where it sits	Standard UK winter weight (IDFL: most common in UK and Ireland)	Top of IDFL's British Standard range, "very cold winters"
Duvets at Dunelm (5 Oct 2026)	27 duvets	5 duvets
Two-piece option	Common: 4.5 + 9 tog sets	Not commonly sold
Best for	Most heated UK bedrooms in winter	Unheated rooms, cold sleepers
Label accuracy	A minimum; may be up to 3 tog higher	A minimum; may be up to 3 tog higher

Making the call

Start with 13.5 tog unless you already know it is not enough. If you own a 13.5 tog duvet and still feel cold on most winter nights in an unheated room, a 15 tog duvet from the same maker is a reasonable step up. If you are cold only on the occasional night, the warmth gap between two labelled ratings may be smaller than it looks.

Where to buy

Dunelm lets you filter its duvets by tog, which makes it easy to compare its 13.5 and 15 tog ranges side by side. Argos, Marks & Spencer and Silentnight also sell winter-weight duvets; our Silentnight vs Slumberdown review compares two value ranges.

For the full seasonal picture, see our tog rating chart by season and our guide to the 13.5 tog winter duvet.