Check out ICF: https://en.m.wikipedia.org/wiki/Insulating_concrete_form https://en.m.wikipedia.org/wiki/Insulating_concrete_form There may be some copyright s

Check out ICF: https://en.m.wikipedia.org/wiki/Insulating_concrete_form https://en.m.wikipedia.org/wiki/Insulating_concrete_form There may be some copyright shenanigans w/ that page. There have also been successfully constructed in-ground pools using this material, but appears to be controversial to traditional pool-builders.