The advent of conductive textiles has allowed the design of much more lightweight and cheaper electromagnetic barriers than used to be with wire mesh and compact materials. Although nowadays it is possible to calculate the Shielding Effectiveness (SE) for wire mesh and compact shields, in case of conductive textiles the scenario becomes more complex. The aim of this work is to find a mathematical model dependent on frequency to determine the Shielding Effectiveness (SE) of several composite materials. Later on, the SE will be found for various sandwich structures of several layers using the previous composite materials and insulation layers between them. This work is structured in 5 chapters. The first chapter shows an introduction to several concepts in the field of electromagnetic interferences. Describes what is EMC, EMS and EMI, defines the most important sources of interferences, how they are coupled into another electronic circuit and the resulting consequences for health of exposure to high frequency electromagnetic fields. Chapter 2 introduces the basic shielding theory concepts and how to calculate the shielding effectiveness. Afterwards, Chapter 3 describes three methods to calculate the shielding effectiveness of different materials such as wire mesh, compact materials and composite textiles. Later on, Chapter 4 characterizes three conductive textile samples that will be used to validate the models described in Chapter 3. Finally, Chapter 5 shows a comparison between the experimental results obtained from measuring the shielding effectiveness of the three samples and the results obtained from modelling the samples with the three techniques in a Matlab environment. The accomplishment of this work has allowed carrying out a technical paper submitted to Radioengineering Journal. The technical paper is enclosed in this document as Annex A.