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

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.