It’s all folded from one sheet of paper to make a four pocket book. Very nifty folding.
Good instructions here
Scale up to a bigger sheet of paper for larger pockets and join two or more fold ups together to make a bigger book.
envelopes
Hedi Kyle Structures
Hedi Kyle is a book structure magician. Her background is in book conservation so many of her structures are glueless and designed to act as supports for other materials – thus making them useful to adapt for object collections, postcards and other emphemera.
This is a comprehensive guide to her structures with making instructions.