Papier-mâché non-inflamable [add borax], graphine-reinforced [strong, hard
   to penetrate], foamed [add baking powder] for lighness and thermal insul-
   ation. See: https://en.wikipedia.org/wiki/Baking_powder [ask Célia]

   Fibre-net strengthened, non-inflammable, foamed papier mâché recipe:

    Old Newspaper
    Plain flour
    Water
    Salt
    Table covering
    Emulsion paint
    Vaseline [for preventing it sticking to its forming container]
    Paintbrush
    Borax [makes it fire resistant]
    Baking powder [to lighten it by foaming]
    glass-fibre or graphine type netting [for strength]

Light weight concrete: All concretes are made with cement, a coarse aggregate, such as gravel, a light aggregate, such as sand and water. The cement uses the water to bind with the aggregates to make bonds that give the concrete its strength and durability. As the name implies, lightweight concrete is a lighter version of the traditional concrete mixture usually used by contractors. It is made by mixing a lighter aggregate, such as perlite, vermiculite or Styrofoam [polystyrene balls] in place of heavier coarse aggregates in with the concrete to reduce the overall weight.