Be interested to see what you’ve got ... the stuff I started out on for making straps as remnants could probably be defined as ‘finest carseat’.. far too soft and rather unpleasant to wear. Whilst I don’t know if that’s the same sort as you have - I suspect most of that ilk had been treated with some protecting type spray/plasticiser.. plain old fresh from the tannery horse/cow seems to work ok.
... what is it you’ve got..? :-)
al