All fabric bags are best made with interfacing and fusible fleece. Interfacing & fusible fleece/batting gives a bag more structure and will make it stronger by strengthening the fabric you make the bag with. No one wants a floppy, thin bag that will lose all of its shape after some use. Not a terribly fancy product but so essential and a must buy if you want to pursue bag making as a hobby or business.
To make A Bag Less Ordinary fabric and leather accessories I use two Vilene products. They are not the cheapest but by far the best I have found and I tried quite a few when I first started my handmade business. The problem I found with other interfacings and fusible fleece is that they made the fabrics I was using stiff and wrinkly. Really not a good look and quite frustrating. So I was so pleased when I finally found the right products from Vilene.
I use Vilene G700 medium weight, cotton, woven interfacing. It's a brilliant interfacing with a lovely drape and adds just enough structure. Perfect for fusing to medium weight fabrics and really easy to fuse using an iron.
G700 is what I use on all the fabrics I make bags from. It works well on a light fabric like a Liberty Tana Lawn cotton and on a heavier upholstery weight cotton too. Using Vilene G700 is always my first step and then I add Vilene H630 fusible fleece/wadding on top. This low loft fleece/batting is really soft and flexible so it doesn't change the quality of the fabric. But it adds some volume and support and a light amount of padding. I fuse this on top of the interfacing and the two together make the perfect pair.
For both of these products you need to use an iron. I use the water from the iron but Vilene advise to use a damp cloth. See the product listing for Vilene G700 interfacing with instructions for use here. And see the product listing for Vilene H630 fusible fleece with instructions for use here. Both products have a layer of heat activated adhesive and that's why an iron is needed to fuse the products to fabric.
Hope this has been helpful and do let me know if you have any questions about these products and how to use them. Both of these Vilene products are available to buy in my shop. I also have a few IGTV videos talking about and using the Vilene product. Take a look here.