What I'm showing you here involves making Half Square Triangles (HST), but papers are available for Quarter Square Triangles and a few other types, too.
I'm making groups of matching HST for a quilt. This paper method is the best for making a bunch of matching blocks, not a whole bunch of scrappy mixed fabric blocks. There are better methods for those. The blocks I'm making require 18 matching 3" (finished) HST. I only need a fat eighth (9" x 20") of each color.
The long skinny package on the left is from Thangles.
The rolled paper is from Triangles on a Roll.
The package underneath that is from Quiltime.
And on the right is a CD from Bear Paw Productions. This actually is something I couldn't part with because I use it to print my own triangle paper. So if I'm in a pickle because I need those triangles when stores aren't open, I do it myself! I included the package of "typing paper" in the picture because that's what I use for printing. Paper that is lighter weight than everyday printer paper is the best because it tears more easily when it comes time to remove that paper. I find this cheapo paper at dollar stores. This package actually is labelled 16 pound (normal is 20). Other packages I have purchased have no info about weight, but once you touch it, you know it's thinner.
Each of the websites above have directions or demonstrations of how to use the paper. The easiest way to explain it without a demonstration is:
Cut 2 pieces of fabric the same size or slightly larger than the paper sheet. Place them right sides together with the paper on top, loosely pinned. Start sewing on all the dashed diagonal lines, then cut on the solid lines. Open the fabric and press.
This is what I am assembling from my triangles and solids. I have a lot more to go. You might think that this is a more time consuming way of making these triangles, and in some ways you are right. But the upside is accuracy. There's no stretchy bias edges to sew, no wonky corners, no marking, no uneven edges to be trimmed. You can make the right size of HST blocks from the get-go, not overcut and then trimmed down evenly.
I found a pretty good way to store my assorted sizes and brands of triangle papers. A magazine file, this one happens to be cardboard from IKEA. Put a label on it and you know where to find those triangle papers every time! I use these files to store a lot more than magazines!