Understanding how genomes fold and organize is one of the main challenges in modern biology. Recent high-throughput techniques like Hi-C, in combination with cutting-edge polymer physics models, have provided access to precise information on 3D chromosome folding to decipher the mechanisms driving such multi-scale organization. In particular, Structural Maintenance of Chromosomes (SMC) proteins play an important role in the local structuration of chromatin, putatively via a loop extrusion process. Here, we review the different polymer physics models that investigate the role of SMCs in the formation of topologically-associated domains (TADs) during interphase via the formation of dynamic loops. We describe the main physical ingredients, compare them and discuss their relevance against experimental observations. Summary key points • SMC-mediated chromatin loops may be formed via a loop extrusion process. • Polymer physics models have been instrumental in studying loop extrusion. • Loop extrusion may be driven by: directed translocation of active motors, diffusion of slip-links, transcription-induced supercoiling. • We describe the main physical ingredients and parameters to better understand and compare these three classes of models.