The tutorial that I used can be found HERE on the Sewplicity blog. I really like her tutorial. I ended up using pre-quilted fabric that I found at a quilt shop in Lancaster, PA last year. You can find pre-quilted fabric at stores locally but the supply is limited. You could quilt your own as she describes in the tutorial or use a home decor weight fabric and add fusible fleece to soften the bag. The "L" I monogrammed using my embroidery machine with the Split Curlz Font from 8 Claws and a Paw.
One thing I did differently was that I used a longer zipper to make a wider bag. My separating zipper was about 26-28" long. After all, little girls pack a lot of clothes, stuffed animals and books to go with them on trips. And it was not hard to adjust the tutorial...you just cut a wider piece of fabric.
Secondly, I did not add the shoulder strap. I just did feel that it was necessary so I left that part out.
Lastly, for the straps, I used a cotton print instead of the same fabric. Using the pre-quilted fabric would have made the straps really thick to sew through and honestly, I did not have enough fabric to do that with. So, I bought some fabric that went well with it and made my straps from that.
Well there you have it, the quilted duffle bag. I hope some of you choose to make one...they are very nice to take with you, especially on short weekend trips!