Comment by DaniFong

we're not aiming to break records with the absolute heat exchanger efficiency, which can get into the high 90s (%) if you're willing to devote a lot of space and mass, but we are innovating in the heat exchanger area. to capture more of the waste heat up to a higher temperature, and preheat the incoming air and possible fuel to a higher temperature, we have to exceed 1000 C and want to drive towards the 1600-1800C maximum working temperature of the high alumina 3d printed material we're using. Thankfully Formlabs has already done some of the preliminary development on the material, but it's bleeding edge both as a material and in use in heat exchangers.