Sewing with wool: suiting, flannel and crepe

Wool is one of the most forgiving fabrics to sew: it eases, presses into shape and holds a crease, and the three types home sewers meet most, suiting, flannel and crepe, differ mainly in how much they fray and how hard they are to press. Pre-shrink the length with steam rather than a wash, sew with a universal 80/12 needle (90/14 for flannel) and polyester thread at 2.5 to 3 mm, and press every seam with a press cloth over a tailor's ham, letting each one cool before you move it. Finish seams with an overlocker or a bound Hong Kong finish, and hem by hand with a catch stitch.

Quick reference: how to sew wool

Which wool is which: suiting, flannel or crepe?

Suiting is usually worsted: the fibers are combed parallel before spinning, so the cloth is smooth, slightly lustrous and firm, between 200 and 300 g/m² (6 to 9 oz/yd²). It frays a little, presses crisply and holds a trouser crease. Gabardine is a worsted twill from the same family.

Flannel is a woolen cloth, spun from shorter, fluffier fibers and brushed after weaving, so the weave is hidden under a soft nap. It is warmer and bulkier, 250 to 350 g/m² (7 to 10 oz/yd²), frays very little, and loses its surface if you press it hard from the right side.

Crepe is woven from tightly over-twisted yarns that spring back and give the pebbled texture and the fluid drape. It is the lightest of the three, often 150 to 250 g/m² (4.5 to 7 oz/yd²), moves and stretches on the bias, and frays more than the other two.

Blends with polyester or elastane behave much the same, with less tendency to shrink and less tolerance of a hot iron. Boiled wool and melton are felted and barely fray at all; treat them like heavy flannel.

Should you pre-wash wool before sewing?

Not in the washing machine: heat, water and agitation together felt the fibers, and the fabric shrinks and thickens for good. Wool does still shrink the first time it meets steam, often 2 to 3 % in length, so pre-shrink it the way it will be pressed later.

The easiest method at home is to steam the whole length. Lay the fabric on the ironing board, hold the iron 1 cm (3/8 in) above it on the wool setting with full steam, work section by section without touching the surface, and let it dry flat before moving it. A press cloth soaked and wrung out, pressed over the fabric a section at a time, does the same with more steam. The older method is the London shrink: roll the fabric in a damp cotton sheet, leave it overnight, then unroll it and dry it flat. If the garment will be dry-cleaned, a trip to the cleaner before cutting also works. The pre-washing guide covers the washable exceptions, such as washable crepes and wool jerseys.

How do you cut wool?

Wool suiting and flannel are easy to cut, with two points to watch. Flannel has a nap, so lay every piece out in the same direction, top to top: brushed cloth looks lighter one way and darker the other. Plaids and pinstripes need matching at the side seams and center back, which usually means cutting a single layer and buying 10 to 20 % extra.

Crepe is the one that misbehaves. It stretches on the bias and shifts under the shears, so keep it flat on the table with nothing hanging over the edge, use pattern weights and a rotary cutter if you have them, and cut one layer at a time for anything larger than a sleeve. Staystitch necklines and the waist edge of skirts as soon as they are cut, a row of regular stitches inside the seam allowance that stops the curves growing while you handle them.

Mark with tailor's tacks or chalk. Wax chalk and tracing paper can leave permanent marks on worsted, so test on a scrap first.

Which needle, thread and stitch length do you use for wool?

A universal needle in size 80/12 suits most suiting and crepe; move to 90/14 for flannel, tweed and anything over 300 g/m². A microtex needle gives cleaner topstitching on a smooth worsted. Polyester all-purpose thread has a little give and is strong enough for seams that will be pressed hard; silk thread is a luxury for hand finishing. Sew at 2.5 mm, lengthening to 3 mm on flannel so the stitches do not sink into the thick cloth, and to 3 to 3.5 mm for topstitching.

Wool rarely needs a walking foot, but it helps where two layers of plaid flannel must stay matched, and on thick seam crossings where a standard foot tilts.

How do you press wool without shine?

Pressing is where wool rewards you. Steam softens the fibers, pressure shapes them and cooling sets them, so the rule is press, hold, lift, and let the seam cool before you move it. Use the wool setting, steam, and always a pressing cloth on the right side: a bare iron flattens the surface and leaves a shine that will not come out. Press seams open over a tailor's ham for curves and a seam roll for straight seams, so the edges of the allowances do not print through to the right side.

Flannel is pressed from the wrong side, with the nap face down on a thick towel so it is not crushed. For crepe, use less pressure and never slide the iron, which stretches it; lift and place instead. A wooden clapper pressed on a hot, steamed edge gives crisp hems and front edges on suiting. How to press seams properly goes through the tools and the order.

How should you finish seams and hems in wool?

Suiting and crepe fray, so finish every allowance that is not enclosed. Overlocking is the quickest. The classic finish for an unlined jacket or skirt is the Hong Kong finish, each allowance bound in bias strips of lining fabric; the Hong Kong seam finish tutorial shows it step by step. Felted wools and dense flannel can be pinked or left raw inside a lining. French seams only work in light crepe; in anything heavier they are too bulky.

Hems in wool are deep and hand-sewn. Allow 4 cm (1 5/8 in) on a skirt and 5 cm (2 in) on trousers, finish the raw edge, press the fold over a cloth, and catch-stitch it so the stitches barely show on the outside. A machine blind hem works on suiting and flannel; a double-fold hem does not, because the fold is too thick. On crepe, let the garment hang for a day before leveling, as the bias sections drop. How to hem has the stitches.

What should you sew with wool?

• A pencil skirt in suiting: the fabric holds the straight line, presses into clean darts and takes a lined back vent well. The pencil skirt pattern is the place to use a worsted with a little elastane for comfort when sitting.
• An A-line skirt in flannel: the A-line skirt hides the bulk of a thick cloth in its flare, and flannel's nap gives it a soft, matte finish that suits winter tights and boots.
• A kimono jacket in boiled wool or a shift dress in crepe: a boiled wool kimono jacket needs no lining and almost no seam finishing. Tailored jackets with collars and lapels are not in Sewly's library yet; the kimono jacket is the closest shape, and its 1.5 cm (5/8 in) default seam allowance leaves room to bind the seams if you choose a wool that frays.