Hi @osuire, Pufferfish is not meant to offset polysurfaces that way, only polysurface faces which is a different thing according to Rhinocommon, that’s why I named it offset surface and described that it can offset polysurface faces. I’ve explained that in a few topics that you’ve been in 
The actual offset Brep wasn’t added until Rhino 6 (Pufferfish supports rhino 5). You can find it in many plugins like Parakeet. Also it is directly in Rhinocommon as a one liner here (R6 only) https://developer.rhino3d.com/api/RhinoCommon/html/M_Rhino_Geometry_Brep_CreateOffsetBrep.htm
Apologies again if the description may have thrown you off!