Quilting fabric for a backpack
 

I'm making a backpack for my granddaughter. We found a pattern that she likes, but she wants the outside fabric to be quilted. I'm planning on using a very thin batting, and I have a couple of questions:
(1) I have both Quilters Dream Poly and Quilters Dream Cotton, both "Request," which is their thinnest type. Is there some benefit to choosing poly or cotton here?
(2) I will be preparing the outer fabric by quilting it first, before I make the backpack. Would there be a reason to back that fabric with muslin as well, or should I just use the outer fabric and batting? Will the quilting definition look different if there is muslin included as backing, or will it just add another layer that will make it more difficult to assemble the backpack?
Thanks!
Carol

It would depend on how much structure and weight you want. The poly would make it lighter in weight when it is finished, but, you would sacrifice some structure to the bag.

I'm also using interfacing that's required with the pattern, so the batting will be in addition to the interfacing. I guess then that the poly might be better because it's lighter, right?

How about you make a few samples? Take 6" or so of the batting and use some scrap cotton that is the same weight, quilt it together and see what you think of it. And while you're at it, try other options such as car headliner, which a lot of people use for bags because it keeps the shape but is soft at the same time.

I made 2 backpacks & used double faced quilted fabric...https://www.fabric.com/quilting-fabr...d-fabrics.aspx and it was so much easier than having to quilt/interface/line, etc. In both cases I had a quick deadline to meet so using the double faced fabric was a great time saver for me.

I have a backpack that is years old and very well used and it is made of upholstery fabric. It has been in rain and snow and survived 20 years plus.

Quilt the fabric, batting and lining fabric together. Trim out the batting from the seam allowances to avoid bulk.

If you are using interfacing, I'm not sure I would use a batting. I would use a backing because of the constant putting things in and out of the backpack. I would probably quilt the top, interfacing and backing (lining) together and then use that for the backpack. I also think this would stand up in the washing, dragging around and general abuse a backpack endures.

This reminds me of something a very, very wise person taught me when my kids were small. She told me to give them each a backpack. Smallish at first and then bigger as they got bigger. The rule was that whatever they wanted to take when we went anywhere, they had to carry! Brilliant! But a side benefit to me not struggling with all their stuff was that it took them awhile to figure out what exactly they wanted to take. This gave me precious time to finish getting myself ready or perhaps having a cup of coffee in peace!