Westlake operates as a manufacturer and marketer of performance and basic materials and housing and infrastructure products. Co.'s segments are: Performance and Essential Materials, which manufactures and markets polyethylene, styrene monomer, ethylene co-products, polyvinyl chloride (PVC), vinyl chloride monomer, ethylene dichloride, chlor-alkali (chlorine and caustic soda), and chlorinated derivative products, as well as ethylene and ethylene co-products; and Housing and Infrastructure Products, which manufactures and markets products including residential siding, trim and mouldings, stone, roofing, windows, outdoor living products, PVC pipe and fittings and PVC compounds.