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The electromagnetic interface shielding properties of poly(methyl-methacrylate) based composite materials filled with hybrid silver-coated glass microfibers are investigated between 100 kHz and 1 GHz using the coaxial cell method. The incorporation of the ionic liquid EMPy-TFSI (1-ethyl-4-methylpyridinium bis(trifluoromethylsulfonyl)) into the composite material leads to a substantial decrease in the percolation threshold and to an enhancement in the electromagnetic interference shielding effectiveness by more than 60 dB. The addition of EMPy-TFSI, selected for its excellent compatibility with the polymer matrix, allows one to obtain composite materials with shielding effectiveness values up to 116 dB, as compared to a maximum value of 43 dB obtained in the absence of the ionic liquid. This enhancement effect is explained by the interactions between the ionic liquid, the polymer matrix and the silver-coated microfibers that lead to a more efficient percolation network. The use of ionic liquids can represent thus a powerful approach to develop functional composite materials with enhanced interference shielding properties.