A hard side shelter is convertible between transport and deployed modes. Existing of the first insulating film and the second insulating film between the electret films and the conductive film enables an increase in electric field intensity in the film when the same electric charge is retained, while enables an increase in surface charge density when the electric field intensity is the same. The skeletal structure may be trimmed and provided with walls to create standard sized filters. Each of the at least two tables is configured to hold a workpiece.