Construction Foam

An industrial “spray concrete,” industrial foam comes in a heavy canister or drum and is deployed with a special sprayer. It is semi-solid and shapeable for about 5 minutes after spraying. Once it fully sets after an hour, it becomes a durable stone-like material. A 1-foot thick (cubic) section of construction foam has an AC of 15 and 40 hit points, but only weighs 10 lbs., roughly 1/15th of the weight of concrete. It is waterproof and takes no damage from cold, fire, acid, poison, or lightning. In industrial applications, it is usually transported via truck.
Price and weight are for a smaller backpack applicator that creates 6 cubic feet of the foam.