A cushioning conversion machine converts a sheet stock material into a relatively lower-density cushioning dunnage product. An exemplary sheet stock material includes two sheets that each overlap a common side of another sheet and are connected to respective lateral edges of the other sheet. The conversion machine includes a forming assembly having a former for shaping and randomly crumpling the sheet material, a set of adjustable guide members to guide the crumpled sheet material to a feeding assembly downstream of the forming assembly, and a severing assembly downstream of the feeding assembly that separates discrete lengths of cushioning. The severing assembly includes a window frame passage that guides the crumpled sheet material to an outlet during operation of the feeding assembly and constrains the crumpled sheet stock material during operation of the severing assembly.