While on the way to discovering just how vital direct mail marketing campaigns are for your business, you may find that you want to probe even further. We encourage and appreciate your thoroughness, and want to help you understand our business just as we take interest in yours. The most practical way to know what we know is to pull the envelope apart (only in theory, of course) and analyze everything you can observe. Let us help dissect the envelope, so you can know as much as we do!

While the parts of an envelope might sound simple and even intuitive, we guarantee you will learn a few things. From front to back and side to side, we will cover every segment of this paper specimen.


Also called the “face,” this is the seamless front side of the envelope. Used to write addresses and return addresses, include postage, the front can be personalized with business logos, brief messages, and windows. (See below for windows.)


Opposite the front side, the back is typically blank, and where the flaps meet.


  • Top Flap- Also known as the “seal flap.” It can come in four different shapes for commercial, wallet, square, and pointed styles of envelope.
  • Side Flap- These flaps are folded towards the center and sealed along the bottom to form a pocket. These flaps vary from wide to narrow and rectangular to triangular.
  • Bottom Flap- The bottom flap is folded and sealed along the edges of the side flaps to form the bottom of the pocket. It may be squarish or more triangular depending on the style of envelope.


The edges of the envelope where the flaps meet and overlap. These vary depending on flap shape.

  • Diagonal Seams- Envelopes with pointed or triangular flaps to create diagonal seams across the back of the envelope.
  • Side Seams- Square or rectangular in shape and close to the outer edge of the envelope. 
  • Center Seam- Found only catalog style envelopes.
  • Seam Overlap- Where the flaps meet and overlap to form the seams of the envelope.


The creases at the top, bottom, and sides, found between the face and the back when all the flaps are folded.

  • Top Fold- Usually scored during manufacturing, the top flap crease is the designated fold for sealing your envelope.
  • Side Fold- The side creases of the envelope that differentiate between the the front and back of the envelope.
  • Bottom Fold- The fold indicated by the crease along the bottom of the envelope. Opposite the top fold.


The space between the top fold and the bottom flap that forms the opening of the envelope.


The space along the throat where the side flaps meet the top fold.


The plastic coated cut-out section that allows a small amount of the inside contents to be read from the outside. These can be customized by shape, position, and with clear or tinted coverings.

Envelope Openings/Closures

As previously mentioned, the top flap is the space left unsealed. The style and position of the flap varies and allows for options in sealing methods. At Worcester Envelope, we offer traditional gum seal, tear-away string, liquid Self Seal, Ez-seal adhesive, and Strip-to-Seal.

At Worcester Envelope Company, we want you to know everything about this small, yet highly effective, medium of communication. The best way to optimize this experience is to understand the medium you are working with. We strive to provide you with the information you seek and take your curiosity seriously at Worcester Envelope Company. No matter the question or concern, we are always (here) for you.