I'm early in the process of making a leather doctor's bag (also known as a Gladstone bag), in this kind of shape:
I've bought a side of ~2mm cowhide for the body, but I know from past experience that it's too flexible to stay in shape while standing on the floor without something to stiffen it.
So, what materials can I use to stiffen the leather in the straight part of the bag's sides?
I've considered the following:
- Card (as used here) - this worries me because it will degrade very quickly when wet.
- Paperboard (chipboard in the US, as used here) - similar issues to card
- Interfacing - I've never seen this used for leather goods but it's a plausible material
- Sheet plastic - this is lightweight and waterproof
- Sheet metal (probably aluminium) - strong, but probably not flexible enough and heavy
- Steel framing (rather than a full sheet) - this seems to be what hard briefcases use for strength but is almost certainly too stiff.
I'm looking for something that will enable the bag to stand upright without sagging, but I'm making a bag not a box, so it needs to retain some flexibility.