Great breakdown on drawing folds!
How to draw folds
Notes on how to draw folds back when I was teaching manga classes back in 2006. From the book “Drawing people” by Barbara Bradley.
This book has a very detailed description of 6 types of commonly seen folds and I think is one of the most educational resource on how to draw folds(Besides Vilppu and Bridgeman).
This is the most amazingly comprehensive guide to folds I have ever seen.