Lego Block Structures as a Sub-Kelvin Thermal Insulator

ICF (insulated concrete forms) are pretty common depending on where you live. You have to build the formwork to pour the concrete walls anyways, so building it to stay in place and act as insulation is just smart provided you can reliably get concrete everywhere you want.

I like them, although for larger structures the formwork gets re-used so generally if they're insulated its after.

I helped a friend build a house out of those foam blocks: it's a lot of fun and you're able to bring a bunch of people together in a "barn raising" tradition that you wouldn't be able to do with traditional construction.

That's how a lot of foundations are poured here. Super clever system.

They tore it down before this important measurement was made.

About $8 / kg. At two grams / brick that's 500 bricks. I'd be more worried about how strong it would be, though I've seen an insanely high tower (15 meters) made out of bricks so presumably they can handle a lot of pressure. If you tried making a 3 x 3 meter wall out of bricks and made it 10 cm thick (a standard clay building brick) that would come to 100 x 300 x 10 bricks = 300,000 bricks, or $6000 worth or bricks! You could hollow out the wall a bit, to maybe 25% dense or even less for a reduction in price.