###### Abstract  
The urge to develop high-speed data transfer technologies for futuristic electronic and communication devices has led to more incidents of serious electromagnetic interference and pollution. Over the past decade, there has been burgeoning research interests to design and fabricate high-performance porous EM shields to tackle this undesired phenomenon. Polymer nanocomposite foams and aerogels offer robust, flexible and lightweight architectures with tunable microwave absorption properties and are foreseen as potential candidates to mitigate electromagnetic pollution. This review covers various strategies adopted to fabricate 3D porous nanocomposites using conductive nanoinclusions with suitable polymer matrices, such as elastomers, thermoplastics, bioplastics, conducting polymers, polyurethane, polyimides and nanocellulose. Special emphasis has been placed on novel 2D materials such as MXenes, that are envisaged to be the future of microwave-absorbing materials for next-generation electronic devices. Strategies to achieve an ultra-low percolation threshold using environmentally benign and facile processing techniques have been discussed in detail. p 202215390117  
signals due to the mismatch of impedance between the incoming EM wave and the metal surface. The presence of free valence electrons in metals paves the way to interact with the microwave radiation and eventually reduces the intensity of the incident waves. However, this creates further EM pollution and is not considered as an effective way to prevent EMI. Numerous demerits viz. poor corrosion resistance, low flexibility and high density further limits their use as EMI shields. Hence, to mitigate this undesired phenomenon, researchers are working in an interdisciplinary fashion to devise high-performance EMI shielding materials that primarily absorb EM radiation. Therefore, EMI shielding of devices using conductive, robust, flexible and lightweight polymer nanocomposite foams and aerogels have attracted researchers in the past few decades [5]. The main criterion for designing polymeric EMI shields with high shielding effectiveness is by inclusion of electric and magnetic dipoles into the system [6]. EM waves, being a synchronous propagation of mutually perpendicular electric and magnetic fields, can interact with the electric and magnetic dipoles, hence reflecting or absorbing the incident EM waves. Owing to the ease of processability, superior mechanical properties, flexibility and tailored functional properties, polymer nanocomposites are potential candidates for designing efficient EMI shielding materials [7; 8; 9; 10; 11; 12; 13; 14; 15; 16]. Effective EMI shields with a predominant absorption mechanism can be formulated by incorporating magnetic and dielectric nanostructures, which will in turn enhance the complex permittivity and permeability of the shields [17; 18; 19]. Numerous polymer nanocomposites with judicious combinations of conducting fillers, such as 1D fillers (carbon nanofibers [20; 21; 22], carbon nanotubes [23; 24; 25; 26; 27; 28; 29; 30; 31], metal nanowires [32; 33; 34; 35]), 2D fillers (graphene [36; 37; 38; 39], reduced graphene oxide [40; 41; 42; 43], hBN [44; 45; 46; 47], MoS\({}_{2}\)[48; 49; 50; 51], MXene [52; 53; 54; 55; 56]), magnetic fillers (Fe\({}_{3}\)O\({}_{4}\)[57; 58; 59], Fe\({}_{2}\)O\({}_{3}\)[60; 61], nickel ferrite [62; 63]) and dielectric fillers (BaTiO\({}_{3}\)[64], barium strontium titanate [65; 66] and TiO\({}_{2}\)[67; 68]) have been extensively studied for designing efficient EMI shielding materials that can overcome the drawbacks of conventionally used metallic shields. In addition, conducting polymers such as polyaniline [69; 70; 71; 72], polypyrrole [73; 74; 75; 76], PEDOT:PSS [77; 78; 79] and polythiophene [80; 81; 82] have also been extensively utilized to shield EM waves. They offer tunable electrical conductivities but have poor processability and film-forming capabilities, which hinders their viability as robust shields.