Boron treated paper. One popular EU make is Isofloc. When building new, you may also want to consider straw bale construction. https://en.wikibooks.org/wiki/St

Boron treated paper. One popular EU make is Isofloc. When building new, you may also want to consider straw bale construction. https://en.wikibooks.org/wiki/Straw_Bale_Construction https://en.wikibooks.org/wiki/Straw_Bale_Construction is slowly improving.