Observational data from WMAP and Planck indicates that Galactic synchrotron emission is significantly more depolarized in the Galactic plane than expected from standard Faraday rotation and turbulence models. While beam depolarization (unresolved structure) and line-of-sight averaging (depth depolarization) explain some of this, the residual depolarization signal implies either an unexpectedly high level of small-scale magnetic turbulence or a distinct, "Faraday-thick" component of the interstellar medium that is not accounted for in current foreground templates (Planck Collaboration 2016; Pasetto et al. 2018).