Re: Milk in Bags?
"[...] unlike those rigid plastic UK milk containers that take up as much space empty as they do full."
Like most plastic bottles they are only sturdy when full of incompressible liquid. When empty they are easily crumpled by hand until almost flat. Only the neck - by virtue of its tubular shape - might need the weight of a foot. The really rigid plastic bottles seem to be for things like caustic cleaning fluids.