What material should be used on the pnumatic shifter air lines...

I don't know the answer with certainty, but I would look at polyurethane pneumatic tubing.  It looks similar and it has properties which I think would work well -- high pressure, flexible but resists kinking, and wide temperature range.

@davidf and @illwillem

I've had the exact same issue with the blipper tube before.  I'm not sure what material Radical use at the factory, but the normal polyurethane pneumatic tube available off the shelf (SMC and Festo both tried) didn't have high enough temp rating (one was rated at 60C at max pressure rating and the other was 80C from memory).  Both companies offer high temp rated tubes, but none of the local suppliers stock that type of tube, and I didn't want 50 meters which was the smallest quantity you could buy (of each size)  I tried thermal shielding which helped it last longer, but I still had a failure where the thermal sleeve touched the tube (so I think where the temperature was most easily transferred to the plastic)... in both cases the blipper stopped working and I found a soft spot (bubble) had formed on the tube where it was too hot and that had burst when the pressure was applied by the solenoid... in my case I could still drive the car back to the pits....

I spent a fair bit of time looking for a supplier of high temperature tube, and then noticed that it was all PTFE (Teflon).  Once I had worked that out I simply started looking for other suppliers of PTFE tube and found some 'Bowden Tube' used for feeding plastic feedstock into 3D printers.  It's available in exactly the right OD sizes to suit both the blipper and gear actuator lines (4mm OD and 6mm OD respectively from memory).  Because the 3D printers run with high temperatures they use pure PTFE tubes and that is what makes them perfect for these applications. They will mostly handle temperatures up to 150C at full pressure... but I think the melting point is over 300C! 

The only small potential issue is that the inside diameter of these tubes tended to be around 1mm smaller diameter compared to the Festo and SMC alternatives.  I was concerned to begin with this would restrict the air flow and maybe cause slower actuation/blipping.  That hasn't been a problem for me.

... and I still use the thermal shielding that I purchased to add another level of protection (in case they get heat-effected over time)

Here's the type I used, but I think any Bowden Tube that is PTFE will work... this s the 4mm OD tube...

https://www.amazon.com.au/Capricorn-Pneumatic-Fittings-Friction-Compatible/dp/B08B7QS77X/ref=asc_df_B08B7QS77X/?tag=googleshopdsk-22&linkCode=df0&hvadid=463557330625&hvpos=&hvnetw=g&hvrand=13303438877647221546&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9072353&hvtargid=pla-945865780498&psc=1

Excellent info Rod! You Sir answered exactly what I needed. I had seen that exact tube in my late night searching and thought it looked promising but to have you confirm it is perfect. Placing an order now. Fingers crossed I can squash this little issue and start to enjoy the car for more than 3 laps at a time. 🍻 🍻 🍻 

RADICAL  PART NO.TP0028  /6MM        TPOO63/4MM    i had same problem  tried few companies on ebay    problem was heat failure        ..never had problem with  original Radical black hose        and  it was really cheap     (cheapest part ive boght from radical )  +sold by metre length   bought 6mts x6mm  1mtr x4mm   cost £12 inc delv   in UK

Thank you for the part numbers Gordon. If the Bowden tube I ordered doesn't do the trick ill pick up the Radical line.