Is raw silk real silk?

Three things the name can mean

• In the silk trade: silk filament as it is reeled from the cocoon, still coated in sericin, the gum the silkworm uses to bind it. The gum makes it dull and slightly stiff. Boiling it off is what gives ordinary silk its softness and shine.
• In Western fabric shops: often silk noil, a matt, nubbly cloth spun from the short fibres left over from silk processing. It is real silk, with a feel closer to cotton.
• On Pakistani and Indian suits: a crisp, textured fabric with irregular ridges running across it, in the manner of dupioni silk. This is the meaning most shoppers have in mind, and it covers real silk and imitations alike.

Why so much of it is not silk

Silk is costly to produce and needs careful cleaning. Polyester can be spun with deliberate slubs and woven to give a very similar crisp, textured face for much less, and it washes easily, keeps strong colour and does not mark with water. For trousers that will be sat in and washed often, many people prefer it. The trouble is only that the same two words are used for both, sometimes with the word pure added and sometimes not.

A blend sits in between: silk with viscose or polyester, or cotton with a silk-look yarn. Our cotton silk and raw silk guide covers how these fabrics wear and how they are stitched.

How to check what you have

If the fabric has no label, our guide to describing unlabelled fabric lists what to note down.

• The label: look for a composition with percentages. Raw silk on its own is a style name; 100 per cent silk is a fibre claim.
• The slubs: in real silk they are irregular in size and spacing. In imitations they tend to repeat at even intervals.
• The feel: silk feels dry and warm in the hand and makes a soft crunching rustle when squeezed. Polyester feels smoother, cooler and more slippery.
• The crease: crush a corner. Silk holds a soft crease. Polyester springs back almost flat.
• The cost: real silk costs noticeably more for the same design.
• Ask for it in writing: the surest answer comes from the seller. Ask for the fibre content on the receipt or in a message before you buy; a seller who knows the cloth will tell you, and one who will not is telling you something too.

Does it matter which it is?

It matters for comfort, care and cutting more than for looks. Real silk breathes and feels lighter on the skin, but it is usually dry clean only and can mark with water. Polyester raw silk is warmer to wear and far easier to wash. Whoever stitches it also needs to know, because the two are pressed at different heats and silk shows needle holes where a seam is unpicked.

So when you send raw silk for Stitching Only, tell us what the label says, or that you are not sure, and include a close photo of the surface. We confirm the fabric is suitable and how much the design needs before you post anything. You can send the details here. For the wider family of names, see our map of silk types, and for judging a whole pack before you buy, our guide to fabric quality in an unstitched suit.