Private company
Who owns Siam Polystyrene Company Limited
One company in the researched set discloses a stake in Siam Polystyrene Company Limited, none of it sized by anyone who discloses it. Siam Polystyrene Company Limited is private, so no 13F reports it: a 13F covers exchange listed positions only. These figures exist because each holder disclosed the stake in its own filings.
Siam Polystyrene Company Limited - Profile
- Type
- joint venture
- Based in
- Thailand
Siam Polystyrene manufactures polystyrene resin in Thailand as one of the four operating companies of the SCGC-Dow Group, the 50/50 joint venture formed in 1987 between The Dow Chemical Company and The Siam Cement Public Company Limited, in which Dow contributes the process technology and plant operation and Siam Cement's chemicals arm contributes the Thai industrial base and feedstock integration. The plant began life at Phra Pradaeng in Samut Prakan in 1978 and was relocated to the Map Ta Phut Industrial Estate in Rayong in 1995, where it takes styrene monomer from the group's neighbouring Siam Styrene Monomer plant. It makes general purpose, high impact and ignition resistant polystyrene grades sold under the STYRON name into home appliances such as refrigerators and air conditioners, information technology equipment and food packaging.
Source
Siam Polystyrene Company Limited files nothing with the SEC, so none of this comes from a filer record. The description was written for this site in August 2026 from Polystyrene, Dow Thailand, About Us, Dow Family Thailand, Dow Inc. 2025 Form 10-K, Exhibit 21 Subsidiaries and SCG-Dow Group announcement (PlasticsNet). The ownership figures below come from the holders' filings instead, and are sourced row by row.
The disclosed stakes
One row per position. Where a holder reports the same company in two share classes, both rows are shown rather than summed, because the class is part of a position's identity.
Where each figure comes from
A private stake has no ownership form behind it, so the source is always the holder's own filing or disclosure. Anything modelled says so, with the arithmetic.
- Dow Inc.. Thai equity-method joint venture (SCGC-Dow Group) manufacturing polystyrene. Percentage taken directly from the 10-K table, which states 50.00 percent; written here as 50.0, not 0.5. No individual carrying value is disclosed: covered by the same combined balance described on the EQUATE row, so value_usd stays null. source
What this page is not
It is not a complete register. It lists the holders who happen to be inside the researched set and disclosed the stake themselves. A private company can have many other shareholders, and nothing here rules them out: venture investors, founders and employees usually appear in no public filing at all. Percentages are of Siam Polystyrene Company Limited where a holder stated one, and are missing where no holder did.