I don't know for sure, I think the frames might be steel but I haven't surveyed them. In any case they're not particularly comfortable, they're extremely Protestant bikes

Ok now I really want to ride a real one, and see how it feels I was gonna hypothesize their steel frames absorbed the jolt of cobblestones but I’m prepared to be wrong

Tyres make a big difference. My alu framed gravelish bike on 35s is a comfy as my Ti framed gravelish bike on 28s. But the weight penalty of those big tyres is real too. And for some reason, lots of bikes come stock with very unsupple tyres.

it’s true, with tires its a dance between weight and comfort