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Just wondering here as my RMax is still on a UPS truck...

Instead of PEEK, why not something like borosilicate glass, quartz, or ceramic? Wouldn't be any problem with them melting, that's for sure.

Borosilicate will hold molten aluminum and stand thermal shocks.

Quartz is very strong but you're pretty much only going to get it in tubes. I switched laser cooling tubes from borosilicate to quartz and never had another break (these covered 4,000 watt lamps and directed cooling water over them...the lamps sometimes explode when they get old).

Ceramic could be made custom, but I don't know what current expenses are.

I machined a heat break from Macor ceramic,,, Worked great but didn't care for the occasional mechanical stress. Currently I'm using stainless tube I threaded this past weekend. still using the teflon tube, which won't balloon if you have a fan running. I bought some pyrex tubing, but it won't slide into the stock nozzles, and I suspect that the filaments may stick to it to much. I'll be testing them shortly.

Been running a 40mm fan design similar to Lightninjays. I ended up doing my own design though it's very similar, just because my CAD skills aren't that good as it was easier for me presonally just starting with the
stock peek cooler base unit. I also modded the adaptor plate and printed in ABS to allow me to increase increase the duct volume.. not sure if its necessary and probably lightninjays is big enough. Very happy with a printed the Adaptor plate
that I'm not going to bother modding the wooden one and stick with it.

So it's been on well over a week now and its superb providing sufficient cooling. So using a Noctua 40mm fan with a 6 year warranty gives me some confidence in failure rates. Also it's attached using the Noctua rubber grommets and I cant feel any fan vibrations when its running.. which is nice
I've done some basic testing and I'd not use a 40mm fan as a layer cooler as the Squirrels are far better. I tried a couple of 40mm designs but the ducting causes too much backpressure for this application IMO.

So if like me you have issues with failing 25mm fans, duct mounting a quality 40mm works really well as it just needs enough airflow.