design idea - boiling hot kettle

Following my recent kettle design project, I can't help wonder why kettles are not insulated to save time and energy when reboiling.  We've all boiled a kettle then not used that water because friends have been delayed etc, then reboiled the water on their arrival to make a cup of tea.  My question would be, would the energy lost in manufacturing kettles with insulated walls be won back with interest, by saving energy on reboiling over the life of the kettle.  Fire risk aside, maybe all current kettles should be given jumpers, just like the traditional tea cosy.