Ultra Pro Silver Size Comic Book Bags are perfect for storing sewing patterns in. That link shows the cost is $5.51 with free shipping for 100 bags which is pretty reasonable. The price does fluctate often so don't think I gave the wrong price if it's different when you click on the link.
This "Silver Size" bag measures 7 & 1/4" X 10 & 1/2" so it holds all the larger, wider or taller sized patterns that seem to be available today. Here are a couple examples
I often buy multiple sizes of the same pattern to accommodate my growing grandchildren and these bags easily hold 2 of the same pattern keeping them together. And this bags size makes it easy to put the tissue pattern pieces back into, yet there's still plenty of room for the new pattern pieces you've made too.
I close the bags with Pattern Fix It Tape which is exactly the same thing as Nexcare paper tape that you can buy at any pharmacy or grocery store. This tape can be opened and closed repeatedly without leaving any sticky residue like scotch tape does. It works fantastic. Anyway, any excess length of the bag is neatly folded over and closed so your patterns look tidy in your pattern boxes and then are easy to flip through.
I have read about using comic book bags before possibly here or other places but they always showed smaller sized bags which would just barely fit the old 'standard' sized patterns. I just happened upon this larger "Silver Size" and was very happy because they are just what I wanted. I have used Ziplocks but they are really sized wrong for sewing patterns. These work so much better and give you a totally clear view. I love them and thought maybe others would too.
Oh, the bags are acid free so they would also be good protection for those vintage patterns some of you collect.