Basics

Fusible interfacing: which one for what?

Thin, medium, firm, fusible fleece, stretch or stay tape: which interfacing goes where, and how to fuse it so it doesn't bubble.

Three interfacings of increasing thickness, below them a blouse with interfaced collar and placket, a bag and a wallet

You can't see interfacing on a finished piece. But you notice right away when it's missing or the wrong one: the collar collapses, the button placket ripples, the bag won't stand.

Interfacing is a thin nonwoven or woven material with glue dots on one side. You press it onto the wrong side of the fabric, and the fabric becomes more stable in that spot. Which one you use depends on how firm the piece should be and what your fabric can take.

Here's which interfacing suits what, and how to fuse it so it still holds after washing.

What you need

Fusible interfacing in a suitable weight
Iron and ironing board
A press cloth (a thin cotton cloth is fine)
A few scraps of your fabric for testing
Fabric scissors or a rotary cutter

Step 1

Thin, medium, firm: the three basic weights

Most interfacings come in three weights. As a rule of thumb: the interfacing shouldn't be stiffer than the finished piece is meant to be.

Thin and soft for collars, facings and button plackets in blouse fabrics. It comes woven or nonwoven. Woven interfacing drapes more softly, nonwoven doesn't fray and is easy to cut.
Medium for bags, trouser or skirt waistbands and button stands on sturdier fabrics.
Firm to stiff for bag bases, wallets and anything that should stand on its own.

Many manufacturers give their interfacings numbers. For nonwovens, “H” numbers are common, for example. That's only a hint at the weight, not a recommendation. Feel the interfacing and lay it on your fabric before you decide.

Step 2

Fusible fleece, knit interfacing and stay tape

A thick fusible fleece and a padded pouch, a knit interfacing with a stretch arrow, and a roll of stay tape placed on a T-shirt's shoulders and hem

Besides the three basic weights there are a few specialists:

Fusible fleece is thick and soft. It pads bags, pouches and laptop sleeves and gives them a soft shape without making them hard.
Knit interfacing is knitted and gives itself. Use it for jersey, for example for facings or plackets. A regular interfacing makes jersey stiff and comes loose as soon as it's stretched.
Stay tape is a narrow strip of fusible interfacing, often 1 to 2 cm wide. It stabilises jersey hems and shoulder seams so they don't stretch out while sewing and wearing.

There's more on wavy hems in 5 jersey traps.

Step 3

Find the glue side and test on a scrap first

Left: the glue dots face up and stick to the iron, right: they face down towards the fabric

The glue side feels rough and is slightly shiny. Hold the interfacing at an angle against the light and you'll see the small glue dots. This side goes onto the wrong side of your fabric, the smooth side faces the iron.

Before you start on your cut pieces, fuse a bit of interfacing onto a scrap of the same fabric. Then check:

Does it hold everywhere, including the corners?
Is the fabric as firm as you want it, or too stiff?
Does the edge show on the right side?
Did the fabric take the heat without going shiny or shrinking?

Step 4

Cutting: slightly smaller, firm interfacing without seam allowance

Left: firm interfacing reaches the cut edge, right: it ends at the stitching line, with the trimmed strip lying next to it

Cut the interfacing from the same pattern piece as the fabric, but not quite as big. If it sticks out past the fabric, it glues itself to the ironing board or the iron.

Thin and medium interfacing: cut 2 to 3 mm smaller all round. It gets caught in the seam and holds there too.
Firm interfacing and fusible fleece: cut without seam allowance, so exactly to the stitching line. Otherwise the seam gets thick and stiff, and corners are hard to turn.

With woven interfacing, watch the grain, just like with the fabric. Most nonwovens don't have one, so you can place them however fits best.

Step 5

Fusing: press, don't slide

Left: the iron slides back and forth and the interfacing wrinkles, right: it rests on one spot with a press cloth, next to a timer

Lay the fabric wrong side up on the ironing board and the interfacing glue side down on top. A press cloth goes over it to protect the iron and the fabric.

Heat as high as your fabric can take. Steam only if both fabric and interfacing tolerate it. You usually get the details for the interfacing when you buy it.
Set the iron down and press firmly, don't slide it back and forth. Otherwise the interfacing shifts and wrinkles.
About 10 to 15 seconds per spot, then lift and set down again, overlapping.
Afterwards, leave the piece flat until it has cooled. Only then has the glue set.

Step 6

Typical mistakes and what helps

Three mistakes: bubbles in the fabric after washing, glue spots on the soleplate and a stiff ridge at the edge of a too-heavy interfacing

Bubbles after washing: too little heat, too little pressure or not pressed long enough. Or the fabric wasn't prewashed and shrank while the interfacing didn't. Wash the fabric first and press longer and harder.
Glue on the iron: the interfacing was glue side up or stuck out past the fabric. Use a press cloth and check beforehand which side is rough.
Edge shows through or forms a stiff ridge: the interfacing is too heavy for the fabric. Choose a thinner one and trim the seam allowance off the interfacing.

For a wallet like Kirsche in woven cotton, testing on a scrap is especially worth it. The outer shell is interfaced, and every bubble shows there.