Shrinkage and relaxation

A garment is not one size. It is a range, and it moves between the ends of that range for its whole life. Two forces do the moving.

Shrinkage

Cloth is woven under tension. Wet it and the yarns relax and thicken; dry it and they stay that way, so the cloth is a little smaller. Every wash does some of this, the first does most of it, and heat does more than cold.

How much depends on the cloth:

• Pre-shrunk (sanforized) cloth has had most of this taken out at the mill. Expect a couple of percent, mostly in length.
• Loom-state (unsanforized) cloth has not. It can lose noticeably more, and the warp — the length of the garment — usually shrinks more than the weft, so a jean gets shorter more than it gets narrower.

Whether a cloth here is pre-shrunk is stated on its material page where it is known; see Raw denim. Wool and waxed canvas are a different story and have their own pages.

Relaxation

The other direction. Worn cloth stretches at the points that bend and bear weight — a jean's waist, seat, thigh and knee; a jacket's elbows. The yarns are not damaged, only eased, and a wash pulls most of it back. That is why a raw jean feels tight after a wash and comfortable a day later, and why a jean that "grew" a size has not — it is waiting for water.

Weight matters: a heavier, denser cloth relaxes less and slower. A lighter cloth gives sooner. Neither is a fault.

What the pattern does about it

Both forces are planned for, not ignored:

• A sample of each new cloth is washed and measured before the pattern is trusted on it, and the master pattern carries a note of the shrinkage allowed.
• A prototype is worn and washed before its finished measurements are recorded, so the numbers describe a garment in use, not one fresh off the machine.
• Where the effect is deliberate — a deep hem that ropes, a waist cut to relax into fit — the project page says so.

The fit consequences of all this are under Why a prototype's fit changes.