The main difference between booklet vs catalog envelopes, plus dimensions of booklet envelopes and dimensions for enclosed print pieces.
250 6x9 Envelopes, Open Side, Latex Self Seal Security Booklet Envelopes, Securely Holds a Small Booklet, Catalog, Card, or Brochure with Strong Self Seal Flap, 250 Side Open White Envelopes
Booklet and Catalog Envelopes - PaperPapers Blog
Booklet Envelope Printing for Custom and Standard Sizes
Catalog and Booklet Envelopes
Catalog Envelopes vs Booklet Envelopes
Booklet and Catalog Envelopes
Booklet and Catalog Envelopes - Design Online
9x12 Envelopes Choose from Window, Catalog & Booklet Envelopes
Minuteman Press [Envelopes (Booklet/Catalog)]
10x13 Booklet Envelopes - High Quality Custom Booklet Printing
10x13 Booklet Envelopes - LA Envelope