When I make spaghetti straps, I prefer to cut them on the bias. This allows me to make them finer, but it has the drawback that bias tends to stretch. Here’s an easy way to reinforce your spaghetti straps so they're strong, but don’t stretch out with wear.

Make your spaghetti straps as usual. When you have finished them and turned them right-side out, simply cut a length of nylon drapery cording the same length as your spaghetti strap. For illustration purposes here, I’ve left the cording longer than the strap. Using a loop turner, thread it through your finished strap.

Put a small stitch at each end to hold it in place until you attach it to your garment. Now your spaghetti strap will be able to handle the weight of the garment without stretching!

Nylon drapery cording is available at most home-dec sewing departments and home improvement stores.