Unsaturated polyester resins: Production route
Two steps: cook a polyester, then thin it in styrene
What this tab covers How it is made: the main production routes or, for product families, the main product types and technologies, compared on share of supply, inputs per tonne, plant scale, yield, co-products and unit cost.All UPR follows the same two steps: make an unsaturated polyester from glycols and anhydrides, then dissolve it in a reactive monomer, usually styrene. The resin families differ in the saturated acid used and in modifiers, which set corrosion resistance, toughness and cost. Vinyl ester resins, made from epoxy and methacrylic acid, are sold into the same markets. Lower-carbon versions use glycols from recycled PET or bio-based sources, and low-styrene formulations cut emissions in use.
Routes compared
| Route | Share of supply | Inputs per tonne | Typical scale | Yield | Co-products | Unit cost |
|---|---|---|---|---|---|---|
| Orthophthalic UPR (general purpose) | 53.31% of 2025 revenue (Mordor via GII) | about 0.35 t styrene, 0.26 t phthalic anhydride, 0.18 t maleic anhydride, 0.27 t propylene glycol (stoichiometric for a 1:1:2 formulation, indicative) | 10-100 kt/yr per site, batch reactors of 10-40 t | about 93-94% by mass after water loss (stoichiometric) | about 0.06-0.07 t reaction water per t, with traces of glycol and styrene (indicative) | not published; raw materials about 80-85% of cost (indicative) |
| Isophthalic UPR | the fastest-growing type, CAGR 6.56% to 2031 (Mordor via GII) | isophthalic acid replaces phthalic anhydride (indicative) | same plants | similar | water | premium to ortho (indicative) |
| DCPD-modified UPR | niche (Mordor via GII) | DCPD replaces part of the glycol and acid (indicative) | same plants | similar | water | low (indicative) |
| Vinyl ester resins (adjacent product) | a separate market of several hundred kt (indicative) | epoxy resin, methacrylic acid, styrene | smaller plants | high | little | well above UPR (indicative) |
| Recycled-PET and bio-based UPR | small (indicative) | up to about 30-40% recycled content (indicative) | existing UPR plants | similar | water, glycol recovered | near ortho when PET flake is cheap (indicative) |
How each route works
Orthophthalic UPR (general purpose)Phthalic anhydride, maleic anhydride and propylene glycol or DEG are esterified in batch reactors, then thinned in styrene. Used for laminating, sheet, artificial stone and SMC.
Cheapest resin; poorer chemical and water resistance.
Mordor via GII 2026; stoichiometry; indicative Isophthalic UPRIsophthalic acid (and often neopentyl glycol) replaces phthalic anhydride, giving better water and chemical resistance for pipes, tanks, marine and gelcoats.
Better durability; higher cost.
Mordor via GII 2026 DCPD-modified UPRDicyclopentadiene from steam crackers is reacted into the polyester, giving low-viscosity, low-shrink resins that need less styrene.
Good surface finish and lower styrene emissions; more brittle.
Mordor via GII 2026; indicative Vinyl ester resins (adjacent product)BPA epoxy resin is reacted with methacrylic acid and thinned in styrene, giving tough, highly corrosion-resistant resins for chemical tanks, scrubbers and some wind blades.
Top corrosion performance; cost and BPA link.
indicative; see epoxy tile Recycled-PET and bio-based UPRPET bottles or polyester waste are glycolysed into oligomer diols that replace part of the phthalic anhydride and glycol; bio-propylene glycol from glycerine can also be used.
Uses waste PET; quality control of feed.
indicative Unit economics are indicative ranges from the sources named; costs move with feedstock and energy prices, plant size and region.