This is a question, we receive quite often: What is the difference between a pressure sealer and a folder-inserter? What are their particular strengths? Simply put, the first produces folded-and-sealed mail pieces, the other outputs a common envelope. But let's have a closer look at it: With a pressure sealer your letter is printed on a custom pressure sealing form which has cohesive glue pre-applied on its edges and can be used just like normal paper in your printer or copy