Bonded leather is a lie.
In the 1950s and 60s publishers began using bonded leather as a replacement for leather on covers of flexible leather books, also known as limp leather bindings. Bonded leather is leather particles mixed with a plasticizer, colored and then pressed with a leather-like pattern. It is to leather what Medium Density Fiberboard is to wood.
The switch was made because it is cheaper than leather, easier to produce, takes less skill to work with, and it sort of functions much like leather. Sort of.
Bonded leather books certainly are fairly flexible:
The problem is that, though it flexes a nice amount, it doesn't have much fold strength. In other words the covers will stay flexible, but where the bonded leather has to bend when the cover is opened it will break. This first shows with a crack along the spine edge of the cover. Not long after these cracks appear the cover will start to separate from the text, often tearing some of the pages off with it.
You can see the crack along the spine of this book. The bonded leather has already broken. All that is holding it together now is the material on the inside of the cover.
There isn't really much publishers can do to solve this problem, it is an inherent flaw in the material. Unfortunately, from the first opening of the book the textblock is fighting the material used to cover it.
At least it smells like leather.
Once a book starts to go it doesn't take long for it get much worse. Here is a book cover which clearly seen better days. This is all compounded by the fact that these books are often well used and well loved. Many of these books are studied and read daily. They deserve better. That is, both the user and the book!
The bonded leather cover can be fixed if it is caught early enough. The repair involves either sewing new endsheets onto the textblock, or strengthing the hinge of the book to keep the cover from coming off the textblock. After doing this a more flexible material can be used on the outside of the joints.
This repair leaves the original bonded leather on the covers and spine. At the end of this, the book can look quite nice, and certainly will last a long time.
But there is a better way.
Over the past few years I've experimented with a way of making a more durable genuine leather cover for these bindings.
The common method of making limp leather covers is to severely pare (thin) the leather. This affects the durability of the binding, though in a different way than happens with the bonded leather. They just wear out too quickly, rather than tear themselves apart.
A few years ago I found a method which allows me to use full thickness leather over the cover of flexible leather covers while still allowing them to flex. They are not initially as flexible as bonded leather covers, but will become that flexible over time. And they have the durability of full thickness leather. They feel great in your hands as well.
Here are a picture of the book shown above after I finished rebinding it.
Basically it has become the book it should have been at the outset.
And it still smells like leather.