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The present work studies the effect of three insect-proof screens with different geometrical and aerodynamic characteristics on the air velocity and temperature inside a Mediterranean multi-span greenhouse with three roof vents and without crops, divided into two independent sectors. First, the insect-proof screens were characterised geometrically by analysing digital images and testing in a low velocity wind tunnel. The wind tunnel tests gave screen discharge coefficient values of C d, φ of 0.207 for screen 1 (10× 20 threads· cm− 2; porosity φ= 35.0%), 0.151 for screen 2 (13× 30 threads· cm− 2; φ= 26.3%) and 0.325 for screen 3 (10× 20 threads· cm− 2; porosity φ= 36.0%), at an air velocity of 0.25 m· s− 1. Secondly, when screens were installed in the greenhouse, we observed a statistical proportionality between the discharge coefficient at the openings and the air velocity u i measured in the centre of the greenhouse, u i= 0.856 C d+ 0.062 (R 2= 0.68 and p-value= 0.012). The inside-outside temperature difference Δ T io diminishes when the inside velocity increases following the statistically significant relationship Δ T io=(− 135.85+ 57.88/u i) 0.5 (R 2= 0.85 and p-value= 0.0011). Different thread diameters and tension affects the screen thickness, and means that similar porosities may well be associated with very different aerodynamic characteristics. Screens must be characterised by a theoretical function C d, φ=[(2 eμ/K p ρ)·(1/u s)+(2 eY/K p 0.5)]− 0.5 that relates the discharge coefficient of the screen C d, φ with the air velocity u s. This relationship depends on the three parameters that define the aerodynamic behaviour of porous medium …