Fundamentally, the largest difference is between the types of adhesive used in the binding process. Perfect binding uses Ethylene Vinyl Acetate (EVA) adhesives whereas (PUR) uses Polyurethane Reactive Adhesives.
The PUR adhesive offers superior adhesion over EVA and also the ability for the bound book to
lay flat without compromising the binding strength. The polar nature of polyurethane molecules allows them to adhere to UV-cured coatings, and films, as well as traditional uncoated and clay-coated papers.
Due to PUR using smaller amounts of adhesive over perfect binding, it also means that you can
achieve a square spine on even the thinnest of books. PUR glue is more durable and flexible than EVA glue and, once the glue has set, it is almost impossible to tear a page out of a PUR-bound book. EVA hot melt glues still have their place in book-binding, especially when it comes to binding thread-sewn books, as the thicker glue allows for greater penetration into the spine area of the folded sections.