Hi pnwdavis,
I’m not sure why that’s happened – would you mind sending me a sample of fabric from that old seat? I’ll email you with the shipping info.
The packraft itself is made with the TPU on the outside, so it will be easy to see if the same thing happens there. If water is somehow part of the cause, that won’t happen to the tube fabric, as water doesn’t get inside the packraft. As a precaution, please do coat all the seam strips and reinforcing strips the Seam Grip+WP on the outside.
For unrelated reasons I no longer purchase fabric from the supplier who made that particular one, so all the new tube fabric is different (you may have noticed that on your new seats), so this shouldn’t be an issue going forward, but if there was a problem with that blue batch, I’ll have to warn others about it and figure out a fix. As I mentioned before, I used that same fabric in one of my boats and haven’t had any trouble with it, but in the packraft the TPU is on the outside, unlike your old seat, so it might not behave the same in that setting (and I used black fabric for the seams etc.).