To make manual splitting in a width direction easy in a plastic foam sheet provided by sticking a flat plastic back film to a bottom surface of a cap of a cap film wherein many caps are formed by hot-forming the plastic film.

The plastic-foam sheet is manufactured by using a film obtained by carrying out inflation of a low speed/high blow ratio either by strongly drawing an ionomer resin as a plastic material by extruding from a T-die, or by extruding HDPE of a low molecular weight from a ring die.