How to determine the stretch percentage of your fabric
Most lingerie items these days will use stretch fabrics (including Sew Projects patterns) so in order to sew lingerie items you need to know how to determine the stretch percentage of your fabric. This is crucial in getting the correct fit so it can’t be overlooked.
Thankfully this is quite simple to do.
Firstly you need to cut a 10cm by 10cm swatch of your fabric you are going to work with. Make a note, or indicate what way the selvedge (or warp and weft if you prefer) would be as you will need to know this when cutting out your patterns.
You need to line the beginning edge up on a cutting mat at 0, or beside a ruler if you don’t have a cutting mat. Firmly hold the fabric down at 0 and with the other hand, holding as close to the edge as possible, pull the fabric as far as it will reasonably go. Look at where the edge reaches to. For every 1cm it stretches to it equals 10% stretch, so the main stretch, perpendicular to the selvedge on this jersey had a 40% stretch as it stretched to 14cm.
The other way only had a small or almost no stretch, so I did not have to test this side.
The stretchier side (main stretch) needs to go around the body (horizontally). Therefore you need to establish which way has the most stretch, especially if both ways are stretchy. For this stretch mesh/power mesh fabric, follow the same principle but test both ways. In the above photo, the side along the selvedge had the most stretch at 35% and the side perpendicular to the selvedge only had 20%. So if the pattern tells you to use the most stretch horizontally around the body, lay the patterns with the main stretch going the same way as the selvedge in this case.
Repeat the same process as above for elastics.
As well as fabrics, elastics have to the have the correct stretch percentage and retention for a particular garment. If your elastic has a different stretch percentage to what your pattern says to use, you could adjust the length of the elastic to compensate.
Stretch retention refers to the amount the elastic springs back after it has been stretched. This is very important in lingerie sewing. If you’re elastic has a poor stretch retention, meaning after it has been stretched it stretches out and does not return the original measurement, then you may not want to use that in areas where the garment needs to be held closely to the body. For instance, the underband of a bra or bralette or the legholes of knickers.
This is the same for fabric, some fabrics are stretchy but their stretch retention is very poor, meaning when stretched out, the fabric will not go back into its original size. It’s unlikely these fabrics will be suitable for lingerie, as you need the fabric to hold its shape well!
If you have any queries on fabric stretch percentage, drop me an email/comment and I’ll be happy to advise you.