I use Space bags all the time. For storage and for mailing and shipping.
The trick to avoid wrinkles is to fold them on the diagonal. The fabric gives and moves on those lines. When you open the bag again there will be no wrinkles. If the quilt looks a little flat a few minutes in a cool dryer will plump it again.
I couldn't live or manage shipping costs without those bags. I don't use expensive ones, just the selection from the local $ Store.
MaryKatherine

I can't get them to work either. I put them in the closet all shrunk down and a few days later I look and they've leaked and everything is falling out of the closet. I'll never use them again.

I agree with above. I have bought and used sets of them twice and each time they have leaked.........and the clothes came out very wrinkled....so-no-mo.......each bedroom (3) has a cedar chest at the foot of the bed and they are "loaded", each quilt is in a pillow case then set into chest.....no problem..have done that for several yrs now......tablerunners, wall-warmers, etc things are in bins in sewing room..........under work tables.........but am running out of room...now what!!!!!!

Space bags work great for me....but I am using the authentic SPACE BAGS. Was amazed when I traveled and used the space bags for clothing, not a wrinkle in anything. No need for the travel iron I took with me. And for single items, used a zip lock bag, which I rolled to take out air, again perfect. I don't understand the science of the whole no air thing, but it works. I would not be afraid to store anything in them.

OK, one more post. If I'm getting this right, you want to use the space bags, to shrink your quilt, to take advantage of the Postal Services Flat Rate Boxes. The main problem I see with your logic, while it sounds spot on, is that when you shrink the quilt, it becomes very stiff. Given that stiffness, unless the quilt is very small, you will have a difficult time maneuvering the quilt into the box. Logically it would work great, but in normal life, not so much. BUT!!!!!! try and see how it works. My visual may be different from your actual. :oIf I have it wrong, never mind!!:o LOL

Quilts are organic...they need to breath.
8. Plastics should generally NOT BE USED for storage. They contain harmful vapors which contribute to the deterioration of the fabrics. Plastics which are particularly harmful: dry cleaner's bags, heavy duty garbage bags, garment bags and Styrofoam.

http://www.museum.msu.edu/glqc/quiltcare.html

I use space bags when I am shipping a quilt, it makes them nice and compact and easier to ship. And contrary to what others think, even though they are "scrunched" when you take the air out, once the bag is opened, the quilt is just fine. Space bags have been a godsend imho!

Quilts are 100% cotton they need to breath. As well as other cotton items.
I would not put them in any plastic bags/containers.

Shipping USPS or UPS is a cheaper way to ship fabrics, quilts, etc. We frequently fly Spirit airlines and they want up to $100 to bring a suitcase. Just shipped a 45 pound box to our destination via UPS for $33 - a real bargain.

You are right. You need to get it into the right dimensions before sucking out the air. My husband and sis used a space bag to take their clothes with them on a carryon since Allegiant air has started charging for carryons, but not for a personal bag. So, they put several things in a small space bag, shrink out the air and stick it into a large purse or a laptop case. Works like magic!

But you do have to start with the dimensions that you want to finish with. You are right in that you can't really fold it after you've taken the air out. It is waay too stiff.