Books and bulky catalogs fit perfectly inside Quality Park Ship-Lite Redi-Strip Expansion Envelopes thanks to the expander. It allows for items to be grouped together in a single package, effectively saving on shipping costs. Plus, the self-sealing adhesive is ultra tacky and flexible to tightly seal even the fullest envelopes. As they circulate into the mail system, the water-resistant surface safeguards against wet weather, so when the package arrives, it's still in pristine, professional condition.