Thickness and mass of laminate

The total laminate thickness is the sum of the thickness of each of its plies:

t_{lam} = \sum_{k = 1}^{N} e_{k} .

Correspondingly the surfacic mass is given by:

s m_{lam} = \sum_{k = 1}^{N} ρ e_{k} .

And the laminate average density is:

ρ_{lam} = s m_{lam} ∕ t_{lam} .