First off, what is a double knit? According to Claire Shaeffer's Fabric Sewing Guide, double knits were an innovation of Italian knit makers. They're stable, knits with little to no crosswise stretch. They're double-faced so they can be used for reversible garments. They're made of wool or synthetics. I personally like the synthetic blends of rayon and polyester, especially for the warmer months.
When can you use a doubleknit? Here's Claire Scaeffer's excellent advice:
For medium and heavy-weight double knits, choose a pattern that suggests a crisp fabric, and if the fabric suggestions do not include double knit, look for suggested wovens, such as linen, wool flannel, and corduroy.
For lightweight double knits, choose a pattern that suggests a soft fabric, stable jerseys, or crepe.
It is frequently better to avoid designs with hard, sharp creases and obvious gathers. Also, double knits cannot be used for patterns labeled "knits only."
Double Knits for Vintage Patterns
Have you ever noticed that vintage patterns often list jersey as a fabric option alongside wovens like chambray and shantung? This is because jerseys of the past - typically wool - were fairly stable, allowing them to be sewn just like wovens. Double knits are similar in body and drape to these vintage fabrics, making them a good fit for a vintage pattern that lists jersey as an option. A single knit or slinky jersey generally won't work well for these patterns because they lack body.
- You don't need a serger to sew with double knits. Sew them just as you would a woven - with a medium length straight stitch.
- However, it's important to use a ball point (stretch) needle to avoid skipped stitches.
- Double knits don't fray so no need to finish the seams - hurrah!
- Be sure to use a silk organza press cloth when pressing because pressing often leaves unsightly shiny spots.
- It's recommended to use a twill stay tape to stabilize shoulder and waistline seams. (I didn't do this on my Background Dress, hopefully it will be okay without.)
- I have used sew-in interfacings with good results. Another good choice is a fusible tricot knit interfacing.
- Cutting double knits is a dream with a rotary cutter.
- You don't need to line double knits.
- Bound buttonholes work very nicely.
One of the best things about double knits is that they skim the body in such a flattering way yet can still have the curve-hugging sexiness of a knit. I found it very difficult to try to fit a garment in muslin that was meant to be made in double knit - the properties of the fabric are just too different. On my current double knit project, I opted instead to cut the pattern with extra-wide seam allowances and then do a basted fitting. This worked well since double knits are a bit more forgiving than a very firm woven.
Buying Double Knits
Gorgeous Fabrics has a nice online selection of double knits (check out this fab hot pink!) I have bought all of my double knits at Rosen and Chadick here in New York. Paron's has a nice selection of wool doubleknits. You can contact any of these sellers for swatches and buying tips.
Hope this info helps you delve into the wonderful world of double knits. As always, let me know if you have any questions!