Animals are organized in a wide range of social structures. Variability in sociality is found both within and among species and is influenced by extrinsic and intrinsic factors. Here we examine the interplay between social behaviour, social thermoregulation and kinship in shaping sociality. We do so for raccoon Procyon lotor, a species suggested to exhibit flexible sociality – from solitary to highly gregarious. We hypothesize that this variation in sociality is driven by environmental conditions, relatedness and their interaction. We used proximity-logging telemetry collars to quantify intraspecific encounters and infer social behaviour among female raccoons. We tested the effect of extrinsic (season and temperature) and intrinsic (pairwise relatedness) variables on proximity. We monitored 15 female raccoons from April 2010 to August 2011, which composed 120 dyads. Daily proximal encounter rate was eight times higher in winter (mean ± standard error: 24.1 ± 4.2) than in summer (3.0 ± 2.6) and daily encounter duration was 12 times longer in winter (558.8 ± 130.3 s) than in summer (43.4 ± 33.1 s). We also found a negative relationship between ambient temperature and proximal encounter rate, which suggested that female raccoons use social thermoregulation as a mechanism to reduce energetic costs in cold environments. Finally, we found that relatedness was positively correlated with encounter rate during summer and winter. Our results suggest that ecological factors, such as seasonality, may affect the evolution of sociality in temperate species, and that the evolution of social thermoregulation in raccoons is likely driven by kin selection.