I ordered my elastic lace off Etsy and opted for 3" width. Now that you have all your supplies, it's time to measure and cut.
Cut the waist band. I am a size 2 (small) so I cut 2 pieces 14.5" long each.
Cut the crotch. I cut 2 pieces 7" long each. This is a little longer than I need, but I prefer working with more material so I can cut down if I need.
Cut the back. I cut 2 pieces 6" long each. Again, this is a little longer than I need.
To make the waist band, lay the two lace pieces on top of each other and pin the ends. Either serger or use the zig-zag stitch to sew both ends. When you're finished it will be a fully closed loop.
To make the crotch, lay the two pieces of lace on top of each other then pin along the middle and move out towards an edge. Sew along this curved line.
When you're done sewing the crotch, just cut off the excess fabric.
To make the back, lay the two pieces of lace on top of each other then pin a curved line that looks like a hill. It's important that one end matches up with the crotch so keep that in mind.
Again, sew along the pin line then trim off excess fabric.
Now cut the cotton fabric in a triangle shape so it matches the crotch section of your undies. Zig-zag sew along all edges EXCEPT the bottom edge which will connect with the back piece.
Sew each section together. I made sure to hold the pieces up to myself during the process to ensure it fits how I like.
Voila! A sexy, yet comfortable lace thong.