How to Prewash Knit Fabric for Sewing (Should You?)
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If you’ve ever been tempted to start constructing your next knit garment as soon as the fabric crosses your doorstep, think twice!
Prewashing knit fabric before starting to sew might be something you dread doing, but if you plan to use that stretch fabric for anything you’ll ever wash, power through and do that laundry right away.
Not sure why?
Here’s why prewashing knit fabric before sewing is important, plus how to wash stretch fabric to minimize shrinking and distortion!
3 Reasons to Prewash Knit Fabric
Unless your fabric is dry clean only, give it a good wash before starting to sew.
1. The Dreaded Shrinkage
First, many knits–those made from natural fibers more so than artificial–shrink A LOT in the first wash, especially in the lengthwise direction.
In fact, since knit fabric fibers are usually not as tightly wound as woven fabric fibers, you’ll find cotton knit fabric shrinking even more than quilting cotton wovens.
You want to get that shrinkage out before you start to stitch.
Have you ever sewn the perfect cotton double knit outfit and then washed it after the first wear to find it only like 90% the size by the time it comes out of the dryer?
(If you absolutely cannot wash your fabric but still want to preshrink, hold a steam iron 1/2″-1″ away from the back surface of the fabric to preshrink.)
2. Chemicals from the Fabrication Process
Washing fabric before sewing removes manufacturing chemicals from the fabric.
My family gets rashes easily from preservatives, chemicals, allergens, and more, so I always prewash to remove these before sewing for my daughters.
3. Colors Bleed
Because dyes can leach out of fabric easily, prewashing lets this happen BEFORE you sew more than one fabric color together.
We’ve all seen new dark wash denim jeans, for example, discolor our chairs, laundry, or even shoes, right?
Avoid this with your knit fabric by prewashing it.
Preparing Knit Fabric for Washing
Now, before you get ready to throw your material into the washer, here’s what to consider.
1. Sort and Test for Color Fastness
I had the worst experience with a red piece of double-brushed polyester fabric I used to make Santa pajamas for my daughters. (Above is the first time my oldest wore the PJs.)
I prewashed the fabric only once before sewing thinking that would do the trick. Oh, how wrong I was.
It was probably ten washes before that red fabric stopped turning my wash pink. The white binding on the pajamas is permanently pink now!
All that to say, sort like colors as you would for everyday laundering so they don’t bleed on each other, and consider more than one wash if you worry the colors will continue bleeding. (One way to assess colorfastness is to cut a small piece of fabric and place it in a clear glass of water and watch what happens!)
2. Minimize Edge Curling and Distortion
One annoying aspect of knit fabrics is washed knits curl more along the cut edges. UGH!
To decrease the likelihood of edge curling, serge rolled edges before washing or baste the edges of the fabric together by hand or machine.
However, if you wash your knit fabric and the edges curl too much, check out my favorite ways to uncurl knit fabric.
3. Assess Shrinkage
If you want to be technical about calculating shrinkage and knowing if your fabric will continue to shrink over multiple washes before your wash the entire piece, experiment!
First, cut a small piece of fabric (like a 6″x6″ square), and wash it with your desired settings.
After washing and drying, measure the final size and compare it to the original 6″ square size.
Continue washing and drying until the fabric no longer shrinks.
How to Wash Knit Fabric Before Sewing
When you purchase your knit fabric, check the label for the recommended washing directions.
While it’s best to follow these instructions, if you plan to wash constructed garments differently, use the washing, drying, and pressing settings you plan to use later on when preparing your knit.
Here are some other things to know!
1. Hand vs. Machine vs. Dry Clean
I machine wash everything I possibly can–busy mom over here!
However, some fabrics, like wool knits, are dry clean only, and delicate fabrics with silk may benefit from handwashing rather than a cycle through the washer.
2. Best Water Temperature and Wash Cycles
To minimize environmental impact, I use cool water, but you can choose the temperature that you prefer.
Warmer temperatures are more likely to shrink fabric, though.
A regular or gentle wash cycle should be adequate also.
3. Detergent Considerations and NO Bleaching
I prefer unscented, healthier detergents without harsh chemicals, especially since having kids. Plus, a milder detergent is also less likely to damage your fabric during the wash.
And, don’t forget that knit fabrics, especially those with Lycra, should also not be bleached.
Not only will the fabric color be affected, but the harsh bleach can break down the fabric’s fibers.
How to Dry Knit Fabrics
Tumbling dry can encourage shrinking and pilling, so if you have patience, a drying rack is an excellent option for smaller yardages.
However, even if it’s best not to dry your fabric, I still dry it anyway! (Simply because that’s how I plan to care for projects I sew from the fabric later.)
Here are a few tips for drying knit fabrics before you start sewing.
- Don’t let the fabric sit in the dryer (or washer, for that matter) for hours before removing it–this isn’t college anymore!
- Wring out extra water after washing to decrease dry time.
- Draping or hanging super wet fabric can introduce distortion or extra stretch, so be careful. We’ve all improperly hung wet clothes before, and they’ve stretched out and had hanger marks, right?
Pressing Knits After Washing
Some knits don’t wrinkle in the wash, but others do.
If you need to remove wrinkles, press with an iron and a pressing cloth. Iron your fabric in a pressing motion rather than a dragging motion, which can stretch fabric.
Also, use a temperature compatible with your fabric’s fiber content.
Fabrics composed of synthetic fibers like polyester or rayon don’t respond well to high temperatures, so be careful not to leave permanent shiny marks from hot, direct heat.
I highly recommend prewashing knit fabrics before sewing so you can discourage shrinking, remove chemicals, and decrease likelihood of dyes running later.
Follow the simple steps outline above, and you’ll be ready to sew your next knit fabric project in no time!