If you have just picked up a fluid, drapey dress from M&S, COS or Reiss and the label is doing you no favours, here is the short answer: silk water-spots but bounces back, viscose loses its shape and strength in rain, and cupro is the quiet over-achiever that handles British humidity better than the other two. With Royal Ascot running 17 to 21 June and Wimbledon opening 30 June, knowing which of the three you have actually bought matters more than the price tag.
Below is a practical decoder: how to read the label, how to identify the fabric by touch in a changing room, and how each one behaves after a full day on grass in unpredictable weather.
Decode the label first (it is sneakier than you think)
Brands love a euphemism. The word silk is legally protected, so unless the label says 100% silk (or gives a silk percentage in a blend), assume there is no silk in the garment. Phrases like silky, silky touch, satin weave or silk-look can legally describe polyester. If a Reiss or Phase Eight slip dress whispers “silky finish” at you, check the composition tab, not the marketing.
Cupro hides under several names. If you see cupra, Bemberg (the Asahi Kasei trademark) or cuprammonium rayon on a COS lining or an Arket trouser, that is cupro. All three words mean the same regenerated cellulose fibre made from cotton linter.
Viscose is usually labelled plainly as viscose or rayon, sometimes as LENZING ECOVERO. It is the workhorse behind most of the fluid summer dresses at M&S, Nobody’s Child, Hobbs and YOLKE.
The in-store touch test
You cannot burn a swatch in the John Lewis changing room, but you can use your hand. Real silk is a protein fibre, so it responds quickly to body heat: pinch a section between thumb and forefinger for ten seconds and it will feel noticeably warmer. Viscose and cupro, both cellulose, stay cooler and feel more uniform in temperature. This is the cleanest non-destructive ID test going.
Then scrunch. Squeeze a handful of fabric in your fist for five seconds and release. Silk springs back with soft, rounded creases. Viscose holds a sharper, papery wrinkle and can look tired immediately. Cupro is the smoothest recoverer of the three; the creases drop out within a minute, which is exactly why it is used as a luxury lining and increasingly as an outer fabric on its own.
Touch also tells you weight. For an occasion silk dress you want momme weight between 19 and 22mm: heavy enough to drape on the body without clinging, light enough to move. Specialist silk sellers list momme; most high street brands do not, so a denser, weightier hand in a true silk dress is your proxy.
The burn test (only if you are already chopping out the label)
This pin showcasing cupro viscose vegan lining fabric provides readers with a direct visual reference for comparing the silk-like drape and sheen of cupro against standard viscose, complementing the article’s home fabric identification tests.
If a scratchy label is coming out anyway, snip a 1cm sliver of the seam allowance and take it to the sink with a lighter. Silk smells of burnt hair and self-extinguishes the moment you pull the flame away, leaving a brittle black bead. Viscose catches fast with a bright yellow flame and smells of burning paper, leaving fine grey ash. Cupro behaves almost identically to viscose in the burn test, because both are cellulose; you can tell cupro apart by its slightly slower burn and finer ash, but for everyday purposes treat the burn test as silk vs everything else. By Hand London and Fabricsight both have detailed flow charts if you want to go deeper.
The rain and humidity verdict for British outdoor events
This is the part nobody tells you at the till. The three fabrics behave very differently when British weather does its thing.
- Silk: water-spots visibly on contact (those tiny dark rings), but the spots fade as the fabric dries. Caught in light Ascot drizzle, a silk dress recovers. Sustained rain is another matter, and sweat marks under the arms can set if you do not blot quickly.
- Viscose: this is the deal-breaker. Viscose fibres lose strength when saturated, which is why a soaked viscose dress can distort, sag at the hem, or even tear at stress points like the underarm or zip. Heavy humidity alone can make a viscose midi droop by mid-afternoon. If the forecast is wet, leave it at home.
- Cupro: the most rain-resistant of the three. It keeps its drape in humidity, resists creasing on a long train journey to Berkshire or SW19, and feels cool against the skin. For a full day on grass in changeable weather, cupro is the quietly sensible choice.
This is the aesthetic Daisy Edgar-Jones often anchors on press tours: that fluid, “silk-look without silk” drape that travels well and photographs softly. More often than not, the fabric doing the work is cupro or a cupro blend, not pure silk.
Want this kind of plain-English styling logic in your inbox each week? The Mūsmūs newsletter breaks down one British wardrobe question at a time, from fabric labels to occasion dressing to the M&S pieces actually worth queueing for. No hype, no clichés, just the reasoning behind what works. Sign up and we will see you on Sunday morning with a cup of tea.
Care: where most expensive mistakes happen
British washing habits (40 degree cycles, optimistic tumble drying) are why so many occasion dresses look exhausted after one wear. Each fabric has a different breaking point.
Silk
Cold hand-wash with a pH-neutral detergent, or a delicates cycle inside a mesh bag at 30 degrees maximum. Never wring. Roll in a towel to remove water, then dry flat away from direct sun (UV yellows silk). Iron on the silk setting while slightly damp, on the reverse.
Viscose
Viscose shrinks aggressively in heat. Oliver Bonas’s UK care guide notes that tumble drying viscose can shrink it by up to 10%, and the same brand surfaces a useful rescue: if a viscose piece has already shrunk, soaking it in lukewarm water with a capful of hair conditioner relaxes the fibres enough to gently stretch it back. Hand-wash cold, reshape on a flat towel, and never put it on a radiator.
Cupro
Cupro has two specific traps. First, dark colours can bleed on the first wash, so if you have just bought a navy or black cupro dress for an event, wash it once two or three weeks ahead, separately, in cold water. Do not buy a dark cupro dress on the Thursday before Ascot. Second, steaming is risky: water droplets from a handheld steamer can land on the fabric and leave dark spots that need rewashing to remove (Marimekko flag this in their care notes). Iron cupro inside-out while slightly damp instead. Cupro blends can also shrink significantly; Fabworks Online notes linen-cupro blends can shrink up to 12%, so always wash cold and air-dry.
What to buy where, and for what
| If you want… | Look for… | Try at… |
|---|---|---|
| A true silk occasion dress with weight and drape | 100% silk, 19–22mm momme if listed | Me+Em, Reiss, dedicated silk specialists |
| A budget-friendly fluid summer dress for dry days | Viscose or LENZING ECOVERO | M&S, Nobody’s Child, Hobbs, YOLKE |
| A polished piece that handles humidity and travel | Cupro, cupra or Bemberg | COS, Arket, Reiss (linings and slip dresses) |
| A “silky” piece for under £50 | Check composition: often polyester | Most high street; weigh against the price |
One thing to do this week
Before any event, do a dress rehearsal at home. Put the dress on, sit down on a kitchen chair for ten minutes, walk around, then check the seat and the underarm for creasing and any sheen change. If it looks tired after ten minutes indoors, it will not survive a six-hour day at Ascot or a queue at Wimbledon. Better to learn that on a Tuesday evening than at 11am in Berkshire car park.
