I was always taught to pre-wash my fabric before sewing with it.
I never asked why, just did it.
Well, I knew some of the reasons why. Namely, some fabric shrinks when you wash it. We would call washing it for that purpose “pre-shrinking”.
So, if the fabric claims to be “pre-shrunk”, do you really need to pre-wash it?
To Pre-wash, or not?
Yes… or no… depending on a variety of things.
Here are a few things to consider:
How do you want to clean or maintain the thing you’re making after you make it? if it’s a garment, do you want to be able to wash it?
Is the fabric even washable? If not, there are alternatives to pre-treat it.
What about interfacing?
There’s conflicting advice out there on pre-treating/pre-shrinking your interfacing.
You don’t have to pre-wash your interfacing.
However, some interfacing may be subject to shrinkage, and if you’re worried about this, you can steam the heck out of it with your iron (don’t touch it with the iron). And see if you get any noticeable shrinkage.
I have yet to have an issue with my interfacing shrinking.
Another thing to consider regarding fusible interfacing.
The chemicals in dryer sheets will dissolve the heat activated glue on fusible things. This includes the glue on fusible interfacing.
So, while that means that ironing a dryer sheet will get the glue residue off your iron when you inevitably get it on there, it also means that fused things can un-fuse when dried with a dryer sheet.
Usually, fusible interfacing is sandwiched between two layers of fabric and sewn around the edges, so there’s little risk of the interfacing being compromised with washes. But you wouldn’t want to allow unprotected fused interfacing to be washed.