Instructions for Interfacing on Bags ... the double edged sword.
I have made hundreds, if not more bags, so this is something I really know about. When I made finished bags for sale, I probably tried every product and every combination you can think of. And still, Interfacing is the conundrum of bag pattern writing.
I don't want you to have a mushy, lightly interfaced bag, and on the other hand, I don't want you to struggle with many layers. I've had to make a decision about how to run with this, and I like to err on the side of not making you break you needles by sewing through 12,000 layers or the stiffest products on the market.
On the new duffle bag, for instance, I decided to have you use a layer of interfacing and a layer of fusible fleece OR use a layer of interfacing and a layer of Annie's Soft and Stable. I'd prefer you use the Soft and Stable. It really performs the way it's named. It's soft (easy to sew through) but it's stable (your bag will have body and stand on it's own). If you use the Soft and Stable, it's a sew-in interfacing. Therefore, you have to use a layer of light interfacing underneath it or your fabric could tear. So, do you now want to interface the lining as well? You totally could. But, in my opinion, you don't have to. That additional layer could be the one that breaks the horses back, or you could really like to have it... I'd be guessing there. So, I decided this time, not to have you interface the lining.
Of course, I do want your bag to stand up nicely. The Soft and Stable does this. However, I also have you do a process of top stitching at the end that helps. And it gives the affect of piping without the layers. You'll press together the outer panels/side seams and do a "Pin-Tuck". Pin tucks are when you fold fabric together like a pleat and stitch them together... But on the bag, I'm simply having you tuck the seam together and stitch on top of it. Here's a picture of what it looks like:
In the end, I have to instruct on the back of a pattern to tell you what you should buy for each pattern. But if I could, I'd put all sorts of buts and ifs with the instructions because what I really want is for you to have choices. Below is a list of interfacings I've used and their basic pros and cons. It really is a matter of what you like, what your sewing machine can handle and what you want to sew through. Happy sewing, and I hope this helps a little in your interfacing decisions.
This gives light body and is great for linings, pockets etc. It's also great for underneath sew-in stabilizers such as Annies Soft and Stable.
Cons: It can't be used alone on a bag... just not enough.
Gives extra body and stabilizes.
It's still pretty light to use alone. And it's not stiff. It might be wise to double layer this product.
Light weight and easy to sew through. Will stabilize bag while keeping it soft.
Very high loft
This stuff is tough. It will make your bag thick and stand up. It is fusible.
This stuff is TOUGH. It will make your bag thick. It's not super easy to sew with. It's fusible, but, often causes wrinkles in your fabric. You have to really take your time fusing this on or possibly use a cotton fusible underneath.
Heavy weight duck or canvas:
When I made finished bags for sale, I had full rolls of fabric backed in canvas professionally. It was fused on with heavy machinery. It really helped to make a nice thick bag that stood up. You can acheive this by making your canvas fusible... simply iron fusible web to the back of the canvas, remove the paper, and fuse to the wrong side of your fabric.
Tough to sew through.
This is a very heavy crinolyn product used in hat making. I love this stuff. It's a sew in product. It is thin, but really stiff, so it's easy to sew through.
While it's easy to sew though, it tends to slip a bit. And because it's so stiff, you'll find it a bit difficult to maneuver through the arm of your machine. You will also have to use a layer of fusible fleece to give it more body.