A pair of British engineers have come up with an instant, permanent, inflatable building in a bag that they call Concrete Canvas -- just add air and water. (Well, OK, not really instant, it takes 12 hours to cure.) A 500lb package turns into a 16m2 (172ft2) building, for around $2,100, about twice the cost of a tent the same size ($1,150) or a quarter of the cost of a comparable rigid shelter such as a Portakabin or Nissen hut (almost $8,000). It can be erected by unskilled labor, can be hydrated using non-potable water, and can even be delivered sterile for use as a field OR. A relief mission can arrive at a disaster site in the afternoon, have buildings erected and curing by sundown, and have a field hospital ready to start accepting patients the next morning.