Brands can choose PVC or TPU valves ;-) I have never seen these issues with the PVC valves. Ozone uses TPU valves. Not sure on F-one. Thanks for that. That explains it. Kite brands that have used TPU valves: Ozone, F-one, RRD, Airush, Liquid Force... TPU is crap (prone to oxidation, and was introdu...