Among cellular materials, Triply-Periodic Minimal Surfaces are promising for thermal management applications because of their high specific surface area, tortuosity, and effective thermal conductivity. In very recent years, additive manufacturing techniques are being employed in designing and printing customized 3D cellular structures, which allow to maximize their heat transfer performance. In applications where convection plays a significant role, monitoring pressure drop is important because of its contrasting role to convective heat transfer enhancement. A CFD analysis of pressure drop in air flowing through gyroid-type structures with different porosities and cell sizes is carried out and presented. Governing equations with appropriate boundary conditions are solved with a finite element commercial code. Velocity and pressure fields as well as correlations to predict the permeability and the Forchheimer coefficient, useful to designers of gyroid-type structures, are presented.