A Yapp bound book has a soft cover ~ limp binding ~ floppy cover ~ with the unbacked cover material ~ usually leather ~ forming the squares.
It is named after William Yapp who was a publisher and bookbinder ~ and member of the Plymouth Brethren Congregation. He popularised this style of binding in the 1860s by using it on his bibles. It remains a popular form of binding on small pocket sized bibles to this day. I read in Wikipedia that the style of binding was in use several centuries earlier. The aim was always to protect the edges of the pages ~ especially bearing in mind that small books were precious and often stuffed into saddlebags or tunic pockets.
A development of this style of binding incorporates a zip such that the entire books is wrapped securely in its own pocket.
Some patience is required when making the book to ensure that the binding folds over to protect the pages. The corners cannot be tailored without cutting and sewing the leather ~ which is quite impractical.
My sub head contains a warning. Everything about a Yapp binding is delightfully straightforward apart from accurately aligning the book block onto the leather. I have tried two ways ~ neither very successful ~ lots more practice required!
The first method is to cut the leather to exact size and paste it accurately to the book block and around the spine.
The second is to take a generously sized piece of leather and trim it afterwards.
In both cases it is difficult to control the amount of glue such that the edges are secure, but that glue does not ooze out in the wrong places.
Give it a try!