While I ended up making the sleeping bag first, the reason why I was inspired to make one is because I actually direly needed a new camping mattress and wanted to see if I could make one.
A while ago I discovered TPU coated fabrics thanks to DIY Packraft . TPU coated fabrics are airtight fabrics and can be used to make inflatable objects if properly heat sealed. The guys at DIY Packraft use it to make inflatable rafts but an inflatable mattress is also definitely an option.
Having discovered that, I bought myself a leather pressing iron, which, according to them, is far more practical to use for heatsealing than a normal iron ( I can now concur) and TPU coated fabric from my favorite outdoor guys at extremtextil.de.
First of course was cutting the fabric which involved a lot of measuring once, twice and even thrice ( and I still managed to fudge it up a bit)
Then, of course I used the leftovers to figure out the proper temperature setting of my iron to get a good seal (https://www.diylpackraft.com/proper-heat-sealing-technique/). According to the guys at DIY packraft a good seal is when you have welded the TPU together without burning your fabric which you can test by pulling the seal open again and checking if there is still TPU on both sides or just on one side. If it's the latter you have a good seal. For an even better seal you then add a reinforcement strip wherever you can.
Having figured that out I went on to actually make my mattress which ended up being a three afternoons job.
First was adding all the baffles on the top of the matress
Then attaching them to the bottom of the matress is when I discovered that given that my fabric was only TPU coated on one side I couldn't do what I had done on the top and first add the baffle and then the reinforcement strip but rather the other way around
Then adding the valve which was ironically a bit daunting because suddenly I was making a hole into something I had been very careful to not make holes in so far.
But I succeeded, and then I proceeded to seal the whole shebang closed. I couldn't reinforce that seam the whole way given that I a) had run out of strips and b) had to do that bit blind. But using the same trick as I used to attach the baffles to the bottom of the mattress, I could reinforce the seams somewhat, which hopefully will extend the life of my mattress.
Then, of course, it was time to inflate the baby and see if my madcap, not entirely thought-through project had actually worked. After quickly resealing a couple of spots, I had apparently missed it turn out that my DIY inflatable mattress actually works. Of course, it has yet to survive a true stress test of sleeping a few nights on it, but it works. It won't win any esthetic prizes anytime soon since my seams, especially at the beginning, are rather wonky, but hey! I made my own inflatable mattress. How cool is that!