I used single wall foaming PLA which has filament density of ~0.45 g/cm3 at 250 degree nozzle temp, about 64% lower than normal PLA. But it is even worse for impact resistance than normal PLA. Weight was the primary driver for this plane
Yep, I've used that as well, but, as you say, it's just very bad for impact resistance. I think the sweet spot between weight and durability might be ABS or something like ASA.
Yes and there is foaming ASA as well which is almost as light as foaming PLA. But I can't print ASA well on my A1 and the weight penalty was still enough that I didn't try, given the mission profile of flight time.
Did I dream or is there even foaming TPU? TPU in general seems almost indestructible to me so should be good :)