If it must be machine washed: what a washable wool duvet gives up
A duvet that has to go in a washing machine needs wool treated against felting, in the weight the coldest night calls for, and that wool costs something in feel and price.
Updated .
In short: Treated wool in a quilted cotton cover, weighted for the coldest night, washed cool on a wool cycle and dried flat or on a line.
The band
| Specification | Source | |
|---|---|---|
| GSM | Light: 200gsm of 100% traceable British wool, approx 2-5 tog. Medium: 350 gsm, given as 7-10 TOG equivalent. A second maker lists Lightweight 300gsm, Approx Tog Guide 4 – 7, and Medium Weight 600gsm, Approx Tog Guide 8 – 14 | light, medium, 300 and 600 gsm |
| Tog band | Makers give ranges, not single values: Light (2–5 tog), Medium (7–10 tog), Warm (11–14 tog). For comparison, British Standard tog ratings range from 4.5 (summer weight duvet) to 15.0 | maker range, IDFL |
| Construction | Wool that has been treated against felting, inside a quilted cotton cover. One warm washable version lists traceable British wool in a quilted percale cover | Woolmark, maker page |
| Size | UK king is 225 x 220 cm. For a duvet that size, one maker advises using a large capacity machine | maker page |
| Care | One maker says machine wash on a 30ºC wool cycle with a wool-safe detergent | 30°C |
Why washing decides the fill first
Untreated wool fibres have microscopic scales on their surface. During agitation in water, these scales interlock which can cause felting and shrinkage. The washing answer therefore settles the fill before the temperature questions do. Machine washable technologies modify these scales to prevent interlocking. The usual method is Hercosett, the most widely commercialised shrinkresist system used to produce machine washable wool, which starts with a chlorine step. One maker writes that its wool is bathed in a chlorine solution to smooth out the natural barbs. The full reasoning is in why most wool duvets cannot go in a washing machine.
What the treatment gives up
The first trade is feel. A patent filing describes the standard chlorine-Hercosett process as one that adversely affects the handle of wool, where "handle" means how the fibre feels in the hand. A second filing notes that after this treatment water repellency is lost and the wool is easily wetted. The second trade is price, because treatment adds a processing step. If you want to see what that step costs, compare a seller's washable and untreated duvets of the same weight. Some sellers say their washable wool skips the chlorine bath, so read the label to see which kind you are getting. Our guide to what a washable wool comforter is covers both kinds.
How your other answers set the weight
Your bedroom temperature still sets the weight. A mild winter room points to the light end of the GSM row, a cool room to the middle, and a cold room to the top. If your summer nights stay cool, one duvet can stay on the bed all year.
Warm or hot summers change that. One duvet cannot cover both ends of the year, so two weights make more sense. One maker's washable range pairs a 200 gsm light duvet with a medium one as an All Season set that joins together. Two lighter duvets are also easier to fit in a home machine than one heavy king. The trade-offs are set out in the two-duvet system.
If wool against your skin bothers you, remember that the fill sits inside a woven cotton cover.
Trying the weight on your bed
Before you wash anything, check that the label says machine washable and not just "hand wash". Then measure your drum against the size you need. Keep in mind that a wet king duvet needs a line or a large flat surface to dry.
Treat tog figures as rough guides. One maker notes that tog values vary depending on the sleeper's body temperature, and makers do not agree on what a given weight delivers. A single weight can span a wide band, as when a seller lists 300 gsm as 4 to 7 tog. Converting GSM to tog explains why makers disagree. After the first wash, run your hand across the duvet and check that the fill is still even and has kept its height.
Further on wool duvets
- Can a wool comforter be washed, and what makes one washable?
- Can a wool comforter be washed, and what makes one washable?
- How is a wool duvet built, layer by layer?
Sources
Outside reading behind this wool duvet page, each entry marked with where on the page it is used.
- light (thewoolroom.com), used under “The band”.
- medium (thewoolroom.com), used under “The band”.
- 300 and 600 gsm (devonduvets.com), used under “The band”; “Trying the weight on your bed”.
- maker range (thewoolroom.com), used under “The band”; “How your other answers set the weight”.
- IDFL (idfl.com), used under “The band”.
- Woolmark (woolmark.com), used under “The band”.
- 30°C (devonduvets.com), used under “The band”.