The timeless appearance and versatility of perfect binding make it the appropriate choice for many book applications. However, perfect binding does have some limitations. For example, the spine can be rather stiff, limiting a perfect bound book’s flexibility. Also, any ink, coating and varnish at the binding edge can compromise the strength of the spine. That’s why we’re often asked, “How can I get the look of perfect binding, but with increased flexibility and durability?”

Our answer is PUR (polyurethane reactive) binding, which holds many advantages over standard EVA perfect binding. PUR-bound books never fall apart. PUR adhesive binding is at least twenty percent stronger than perfect binding, and the greater spine flexibility gives PUR-bound books lay flat capabilities. PUR adhesive is impervious to ink, varnish, UV and aqueous coatings, which makes it an ideal choice for applications that have these elements bleeding into the spine area. PUR binding requires a thinner coating of adhesive, which makes it preferable for very thin books. Here are a few additional applications that call for PUR binding:

• Books that are used frequently and heavily.
• Books that will be used in extreme temperature conditions.
• Very thin books (those bulking 1/8” or less)
• Signatures that are printed with the paper grain perpendicular to the spine.

Planning for PUR binding projects is similar to that of perfect binding, but with a few exceptions. Keep these tips in mind to be sure production of your projects goes smoothly:

Curing time - Unlike standard EVA perfect binding, PUR adhesives are cured by the moisture in the air (so yes, they cure faster on very humid days!). For that reason, PUR-bound books require at least 24 hours to fully cure.

Testing - Due to the extended curing time required for PUR adhesive binding, page pull testing performed during binding will not be accurate. Instead, strength tests on PUR books are typically performed over a period of several hours to gauge the strength of the bind as it cures. One way to tell if PUR glue has cured is to bend back the book at the center spread. If there are visible glue strings in the spine along the entire binding edge, you’ll have a very strong bind.