2 Hard Leather. Poor chainmail, studded leather. Note that for living things, Mass, Volume, and Strength are all equal on average by definition. For machines, things are different. Strength could be broken into Structure and Power.
Structure is the ability to bear load without collapsing.
Structure is higher in metal machines than in living things of the same Mass. Power, as defined here, is the ability to actually move the load around. Power can be higher or lower than in a living thing of the same Mass, depending on the design of the machine. Volume varies widely, again depending on the design. Also keep in mind that given weight statistics for vehicles will include armor weight, so the estimated Power and Structure should be reduced. If using extra strength to carry heavier armor, add Strength Scale to listed values.