trash monkey

When doing a garment where the fit relies on stretch, you want a mockup fabric with as similar of stretch as possible so that the mockup will fit similarly to the actual garment. If you use something with significantly more or less stretch and base the fit off of that, you will risk having a too tight or too baggy final garment.

Thankfully, garments made of most spandex-type knits have a decent amount of leeway in fitting, and a lot of fitting can be done after it is cut. I’ve been able to do mockups with less stretch than the final garment (stretch crushed velvet is cheap enough to do this with) with no problems because I just adjust the fit in the final garment, but if you aren’t comfortable with doing that, be sure to get similar stretch. This is why, when working with most spandex where there’s difficult fitting issues, I’ll buy extra, so that I know I have enough fabric to make a mockup in the same material.

If doing something like planning colorblocking on a bodysuit, you especially want to make sure your stretch is similar so that the pieces will be the correct size once pieced together.

If you are using a stretch woven or other material without a lot of stretch where the fit doesn’t depend on it and where the stretch is just there for comfort, you can use a non-stretch mockup material.

If the fabric is stretchy but it doesn’t control the fit (like with a loose garment), try to use something with a similar drape, but a similar stretch isn’t as necessary. Something like a loose t-shirt would fit differently in a jersey knit vs. a stiffer muslin, despite not having the fit controlled by the stretch, so be sure to account for that.