The Navajo 3-ply technique (AKA Navajo plying, or chain plying) is typically used during the yarn spinning process, but it can also be used to triple the thickness of your working yarn without having to use 3 skeins at once. For instance, if you have a lot of a sock weight yarn but you want to work up a pattern that calls for aran/bulky yarn, you can use the thin yarn anyway with this method.
how to do it
Set up your yarn like this:
Now reach through the loop with your fingers and pull the working yarn through. You’re essentially making a giant chain with your fingers. I usually pull it as far as my arms can reach, but for photographic purposes I made a shorter one: