hello dear DrWelby hello Gudan,
first of all: many thanks for the quick reply and for all the ideas that you share
The material on the Ortlieb seat bags is similar to what is sold in the US as "heat-sealable nylon". It can be bonded together using a clothes iron. You can find instructions on making simple things like dry bags with it. I'm not sure how easy it would be to make bags with tighter corners. I plan on trying it out eventually - it is quite a bit lighter than the vinyl-coated polyester than I can get.
did you try it out yet!? i would love to hear from you again
I make bags myself and I can tell you what is made of what. Ortlib makes pvc bags, it is welded with a hot air gun and glues very well, nothing cracks and the seams are very well sealed. Here are my works you can see
https://www.instagram.com/bike_and_bags/ or on my website, for example, here on the trunk a bag looks like it is made of PVC
https://bikeandbags.eu/work/velosumki-bagazhnik-20l/ The bags are also made of TPU coated with nylon or polyester, this material does not adhere well and is usually HF welded. Light bags are usually made of this material, but they are expensive.
many thanks Gudan for sharing your ideas and plans - awesome. Very great.
i would love to create a ortlieb frame bag