DID YOU REMEMBER THAT MADE TO MEASURE LEGGINGS ARE COMING??
You will need 1.5-2 yards of stretch fabric that exhibits at least 10% stretch AND stretch recovery.
The easiest and quickest way to ensure that it has these properties is to buy anything with at least 5% spandex. The long way to figure it out is to do a couple of stretch tests. For the nerds out there, check it out, there’s an ASTM standard for fabric stretch testing.
For those of you who are not standards nerds, I dug up some photo and video tutorials of tests I have used:
Basically, this refers to how much the fabric will extend to provide you with coverage and the ability to move. A 10 inch piece of fabric with 10% stretch will stretch to 11 inches under tension. (It will stretch an extra 10% of its total length, get it?)
Another way to look at it might be, if L=length of fabric, and S= stretched length of fabric:
Where x = your stretch percentage converted to decimal
Recovery is how well a fabric returns to its original size after being stretched. NOBODY LIKES DROOPY LEGGINGS. You want to be able to squat down, stand up, and have your leggings look the same the entire time.
And finally, some examples of suitable fabrics (from a variety of sources).
… wow I guess I just really like grey… YOU’RE WELCOME