We have studied the effect of different diisocyanate cross-linking agents on the electro-optical properties of cellulose derivative based PDLC type cells and on the dielectric properties of the films used on their preparation. Each optical cell was assembled with a cross-linked film produced with a different type of diisocyanate and with the nematic liquid crystal (U). One was assembled with a non cross-linked film. The six different cells were then analysed by light transmission and the results were correlated with the dielectric properties of the cellulosic films used in each one of them. It was found that the cell with the higher contrast is the one prepared with the film cross-linked with 1,4-diisocyanatobutane (BDI) [6]. Based on the results obtained, we propose a mechanism to describe the electro-optical behaviour of these systems.