PUR (polyurethane reactive) is the strongest binding glue available. It is very similar to perfect binding in that text sections are folded with perforations at the spine which allows the glue to seep into the pages giving a strong bind.
As with perfect binding, it gives a very neat, professional finish. It is suitable for publications of around 48 pages or over as the spine needs to be of a minimum thickness to glue into. This makes it especially suitable for very thick books, or catalogues and brochures that will be used frequently.