Sketch explaining the processes that facilitate the formation of the snow line pile-up: a) in the initial condition, ice increases the solids density outside of the snow line; b) coagulation is more efficient for aggregates that incorporate water ice. Thus, solids grow to larger sizes and drift faster outside of the snow line. The quick drift results in an efficient delivery of the embedded refractory material, which does not drift rapidly, causing a “traffic jam” and increasing the dust concentration in the inner disk; c) the outward diffusion and recondensation of water vapor locally enhances the abundance of solids just outside of the snow line, contributing to the pile-up of icy pebbles.