Adding a strip of cotton tape to seams can do a number of things.
- It acts as a stabilizer when sewing with knit/jersey fabrics. It prevents over stretching and stitch breakage.
- Helps prevent seams coming apart if the fabric is prone to fraying
- It may provide support to fabric cut on the bias or gathered pieces.
Match your fabric right sides together as you would normally and then place cotton tape on top of fabric layers. The tape comes in a range of widths so you would need to match your seam allowance. Basic colours are white & black.
Pin and sew as normal.
This will thicken your seam somewhat so you may need to trim or grade.
Also, if you are using a pre-washed cotton fabric then you may need to pre-shrink your cotton tape too.