Should you stretch elastic when sewing? Before answering this, let me reminisce…
I remember the first time I sewed lingerie. I was in my apartment in West PhillY and I was in my mid twenties. I had sewn the side and the gusset seam and I was ready to attach the picot elastic at the waistline and leg opening. Gripping either end of a strip of elastic, I stretched it. “It stretches, so I should stretch it!” Oh how I wish I still had those pair of undies. They turned out so fugly ; )
Is there a percentage you should undercut an elastic? Should you take into account the stretch percentage of different types of elastic? Yes, there is math you can use and marks you can put on your sewing machine, which I will go over below. This is super helpful if you’re a new lingerie sewer because it will help you develop an intuitive sense over time. After about a year of sewing lingerie of different fabrics and different elastics (there was a lot of trial and error!), I developed a sense of how much tension to apply for each garment or application. Now, I may do a test run before sewing a new quality of elastic or fabric, but for the most part, I don’t use any math, marks, or pins.
First, let’s go over different types of elastic. Lucky for you, there are over 60 elastics listed in the lingerie elastic section of the web shop. I personally think the trimmings kits (there is black, white, blush pink, red and beige) are great because you get all types of elastic needed to make a bra and underwear in 1 kit.
Types of elastic: I believe that choosing elastic is so hard because you’re not exposed to it. Craft stores don’t stock it and a few online vendors sell it. How are you supposed to know what to get if you’ve never seen it before.
1/4” panty elastic: generally used for finishing waist and leg openings on a panty
3/8” picot plush back: generally used for finishing the armhole, neckline and/or top back band on a bra or bralette
1/2”-5/8” picot plush back: generally used for finishing armhole, neckline and top back band on a bra or bralette for larger band/cup sizes (it provides more support).
3/4” picot plush back: generally used for finishing the bottom of a bra or bralette
1/8 spaghetti – 3/8” elastic shoulder strap: generally used for shoulder straps for smaller band/cup sizes
Fold over elastic: generally for finishing panties, armhole, neckline and top back band on a bra, bralette, and undie.
Sewing elastic: for new lingerie sewers, using math or marks on your machine will be a huge help. It will also help you develop an intuitive sense of how much tension to apply over time. Something to note is that elastic can be “fatigued”, which means that it can be only stretched to a certain point. Think about it – the more you stretch elastic, the more holes you are putting into it. This can cause an elastic to be wavy after sewing, although I find the quality of the elastic to be the culprit most of the time.
Using Math: Generally, elastic is stretched between 3-8%, with 8% being used only in parts where you want the garment to “hug” the body (i.e. at the underarm near the armpit). So if you want to use math, then you can measure the length of what is being sewn and reduce it by 5%. When sewing, pin it at the half and then the quarter so that equal tension is applied. **If you’re using non stretch fabrics, especially on a panty, then you will need to reduce the elastic more than this to ensure that the panty can fit over your hips.
Using Marks: You can also put marks or tape on your sewing machine and use them as guidelines or points to where to pull your elastic to when sewing. I recommend tape so that when you develop an intuitive sense, you can remove the tape.
Using Intuition: I don’t use any calculation, marks or pins, and have developed a “feel” for how much to stretch elastic, which you will too with practice ;)