Interfacing is a used to make fabric thicker & firmer, and to help stabilize pieces during sewing.
It is used in many sewn accessories to add structure and make the fabric thicker. In clothes interfacing is often used in cuffs, collars and shirt facings.
There are two types & two styles of interfacing: woven/non-woven & fusible/sew-in.
:::: Woven Interfacing :::
This type of interfacing has visible threads and looks much like regular fabric. Like fabric, woven interfacing has a grain that should be followed during cutting.
I prefer woven interfacing because the fusible kind doesn’t tend to bubble and wrinkle as much as the non-woven fusible.
:::: Non-Woven Interfacing ::::
Non-woven interfacing is made from fibers pressed together. It has a gauze-like appearance and usually has a stippled texture. This interfacing is useful in clothing construction, but I never use it for accessories. It is very easy to melt into a useless mess of wrinkles, and I find it separates from the fabric easily.
:::: Fusible Interfacing ::::
This type of interfacing is applied to the fabric using an iron to melt the adhesive side of the interfacing to the fabric. The adhesive side is the shiny side, and it needs to be placed with the adhesive facing the wrong side (back side) of your fabric.
When you purchase iron-on interfacing the fabric store will usually include the manufacturer's instructions regarding iron temperature and press time.
When applying iron-on interfacing don’t move your iron around like you are pressing wrinkles from the fabric. Simply heat up your iron to the recommended temperature, and place the iron face down on the wrong side (non-adhesive) of the interfacing in one spot. Leave the iron in place for the recommended time and then move it to the next section. Continue until you have adhered the interfacing to the entire fabric piece and then leave the fabric in place (as in don't move it) until it has cooled.
If your fusible interfacing seems to be shrinking a lot and wrinkling, give it a good shot of steam before putting the iron down on it. The heat from the steam will help shrink it before you adhere it in place.
When using iron-on interfacing, I usually cut the pieces about 1/8" smaller than the fabric piece. This gets rid of some bulk in the seams, but most importantly it keeps the edges of the interfacing from creeping past your fabric edge and adhering to your ironing board. It might not seem like a big deal, but as time goes by the interfacing adhesive collects on your ironing board and ultimately transfers to your iron. This black gunk then ends up on your fabric and doesn't do your iron any good either.
:::: Sew-In Interfacing ::::
Sew-in interfacing does not have an adhesive side. It is placed on the wrong side of the fabric and then pinned, or basted, in place rather than adhered with adhesive.
Sew-in interfacing is generally woven (though I think non-woven is available), so it has a definite fabric grain that should be followed during cutting. Always launder sew-in interfacing before use.
I'm becoming a big fan of the sew-in interfacing, especially for bags and larger accessories. Sew-in interfacing doesn't offer quite the firmness of fusible, but overall it is less
expensive than fusible, has fewer chemicals, can be laundered, and it is far less likely to cause your fabric to pucker or wrinkle.