Methods of forming a sheet-form product can include: providing a forming surface having a multiplicity of inwardly extending forming cavities; forming a multi-layer sheet in the interior of which is a parting surface defined by materials of limited compatibility, material of the sheet lying on each side of the parting surface having peelable tensile strength; pressing the multi-layer sheet against the forming surface to cause the multi-layer sheet to substantially conform to and fill the cavities; and peeling the multi-layer sheet apart at the parting surface, whereby material directly engaging the forming surface defines a sheet-form member having a multiplicity of hollow formations.