Abstract: An electrically heated furnace assembly, suitable for a hot isostatic press, having windings of one or more resistance heating elements, helically wound about the longitudinal axis of the furnace assembly; rigid insulating sleeves, enclosing the heating elements and substantially covering their surfaces; the insulating sleeves abutting against the leading and trailing edges of one another and against the outer, upper and lower surfaces of one another; and a spiral shelf provided about the longitudinal axis of the furnace assembly, underlying the heating elements, and abutting against the outer lower surfaces of the insulating sleeves which enclose the lowermost winding of the resistance heating elements.