There is a belief that in order to sew Lycra, it is essential to use elastic thread, woolly nylon thread, or transparent thread. However, after more than 20 years of making rhythmic gymnastics leotards, my recommendation remains to use a good polyester thread.
Why?
Because it is strong, durable, and perfectly withstands the intensive use that leotards are subjected to during training and competitions.
Furthermore, when seams break or pop, in most cases the problem is not the thread, but an incorrect machine setting.
The secret is in the stitch and the tension
If there is something truly important when sewing Lycra, it is ensuring that the seam has the ability to stretch.
To do this, I recommend using a narrow, short zigzag stitch, creating a shape similar to a small accordion.
This structure allows the seam to follow the elasticity of the fabric when the gymnast moves, avoiding breakage and unnecessary tension.
Many people try to solve this problem by using elastic or transparent threads, but the reality is that a well-configured seam with polyester thread offers excellent results.
What is truly important is to correctly adjust the machine tension and perform prior tests until achieving a flexible stitch that can stretch along with the Lycra without breaking.
The importance of choosing good Lycra
The quality of the fabric is as important as the construction itself.
Good Lycra should stretch correctly in both directions and, above all, have excellent recovery capacity.
That is to say, it must return to its original shape after being stretched.
When Lycra does not have sufficient recovery, deformations, fabric bags, excess looseness, and a progressive loss of the leotard's fit appear.
That is why I always recommend investing in quality Lycra. A fabric with good elasticity and good recovery facilitates construction, improves the fit, and considerably increases the durability of the garment.
My advice after 20 years of making leotards
If I had to give one piece of advice to someone starting to sew Lycra, it would be this: don't obsess over looking for special threads.
Use good Lycra, quality polyester thread, a suitable needle, and spend time correctly adjusting the tension and the zigzag stitch until you achieve that accordion effect that allows the seam to follow the movement of the fabric.
That is the difference between a seam that lasts for years and a seam that ends up popping on the first use.