Why Royal Navy armour weight complicates thickness comparisons

Isn't Chobham armour thicker for the same weight per area?

The comparison hinges on Royal Navy specifications in pounds per square foot, with thickness inferred from the expected material.

The follow-up challenges the assumptions used for the armour substitution. The Royal Navy's specifications are described in pounds per square foot. A stated thickness can therefore be an estimate derived from the expected properties of the plate. Changing the material means that its thickness cannot simply be carried over without considering the weight specification. The short answer leaves the composite-armour comparison qualified.