EXHIBIT 21

SUBSIDIARIES OF WESTLAKE *

Name of Subsidiary |  | State or Other Jurisdiction of Incorporation or Organization |  | Names Doing Business
North American Pipe Corporation |  | Delaware |  | North American Pipe Corporation and NAPCO
Westech Building Products, Inc. |  | Delaware |  | Westech Building Products, Inc.
Westech Building Products ULC |  | Canada |  | Westech Building Products ULC and Westech Building Products Limited
Westlake Ethylene Pipeline Corporation |  | Delaware |  | Westlake Ethylene Pipeline Corporation
Westlake Longview Corporation |  | Delaware |  | Westlake Longview Corporation
Westlake Management Services, Inc. |  | Delaware |  | Westlake Management Services, Inc.
Westlake Petrochemicals LLC |  | Delaware |  | Westlake Petrochemicals LLC, Westlake Petrochemicals LP and WPE
Westlake Polymers LLC |  | Delaware |  | Westlake Polymers LLC, Westlake Polymers LP and WPE
Westlake PVC Corporation |  | Delaware |  | Westlake PVC Corporation
Westlake Styrene LLC |  | Delaware |  | Westlake Styrene LLC and Westlake Styrene LP
Westlake Supply and Trading Company |  | Delaware |  | Westlake Supply and Trading Company
Westlake Vinyls Company LP |  | Delaware |  | Westlake Vinyls Company LP
Westlake Vinyls, Inc. |  | Delaware |  | Westlake Vinyls, Inc., Westlake Monomers and WCAO
WPT LLC |  | Delaware |  | WPT LLC and WPT LP
Suzhou Huasu Plastics Co., Ltd. ** |  | People’s Republic of China |  | Suzhou Huasu Plastics Co., Ltd. and Huasu

* | Westlake has elected to omit the names of certain subsidiaries. None of the omitted subsidiaries, considered either alone or together with the other omitted subsidiaries of its immediate parent, constitutes a “Significant Subsidiary” as set forth in Section 601(b)(21) of Regulation S-K.

** | Westlake owns 59% of this entity but accounts for it using the equity method.