At a glance
| What this is | Tin(II) 2-ethylhexanoate — the gel ("setting") catalyst in flexible polyurethane foam, used with amine blowing catalysts to turn liquid polyol and isocyanate into solid foam |
| CAS number | 301-10-0 |
| Carcinogen status | Not classified as a carcinogen. The concerns are cytotoxicity, residual tin, and its VOC breakdown product |
| Key hazards | Cytotoxic in vitro; degrades to 2-ethylhexanoic acid (EU CLP reproductive toxicant, Repr. 2); residual tin persists in cured foam |
| Where you encounter it | Flexible PU foam in mattresses, toppers, pillows, cushions, and carpet backing — as a residue and via its off-gassing acid by-product |
| Sleep micro-environment relevance | A catalyst residue in the foam you sleep on and a documented contributor to flexible-foam VOC emissions |
| Where it is heading | Active replacement by non-toxic bismuth catalysts and reduced tin loadings to cut VOCs |
What it is
Polyurethane foam is made by reacting a polyol with an isocyanate, and that reaction needs catalysts to happen at the right speed. Flexible foam uses two kinds: amine "blowing" catalysts that control the gas expansion (see BDMAEE, DMEA, TEDA) and a tin "gel" catalyst that drives the network-forming reaction. Stannous octoate is the classic gel catalyst. Peer-reviewed — El Khezraji et al. 2021
Unlike a reactant, a catalyst isn't consumed — so much of the tin remains in the finished foam. Spectroscopic study of cured foam confirms that tin-octoate residues persist, shifting oxidation state as the foam ages, with its octanoic/2-ethylhexanoic acid by-product detectable in the material. Peer-reviewed — Labouriau et al. 2006
How it relates to the bedroom
A residue in the foam — and a source of its VOCs
The bedroom relevance is twofold. As a residue, the tin catalyst stays in the mattress foam, and stannous octoate is cytotoxic in laboratory cell tests — measurably toxic to fibroblasts and human endothelial cells, more so than the common amine catalysts. Peer-reviewed — Tanzi et al. 1994
As a VOC source, the tin catalyst is a direct contributor to what new foam off-gasses. Foam-industry research on flexible slabstock — the foam in bedding, furniture and carpet — found that once amine-catalyst emissions are addressed, the main remaining VOC is 2-ethylhexanoic acid originating from the stannous octoate, and cutting the tin catalyst lowered total VOC further. Peer-reviewed — Rothe et al. 2001 That 2-ethylhexanoic acid is classified in the EU as a reproductive toxicant (Repr. 2). Regulatory — EU CLP harmonised classification of 2-ethylhexanoic acid (Repr. 2, H361d)
Keeping it in proportion
This is a residue and low-level-VOC story, not an acute hazard — household exposure from a cured mattress is far below the levels behind the cytotoxicity data, and the tin itself is relatively immobile in the foam. Inferred — bound catalyst residue and dilute VOC emission imply low household exposure relative to the in-vitro test concentrations The honest framing is that stannous octoate is one of several reasons new foam off-gasses and a legitimate target for cleaner chemistry — not a reason to fear a mattress you already own, especially once it has aired and de-gassed.
The regulatory picture
Stannous octoate is governed mainly through general chemical law and product VOC/emissions standards rather than a bedroom-specific ban.
Chemical classification. The catalyst is registered under REACH; its reproductive-toxicant breakdown product, 2-ethylhexanoic acid, carries an EU CLP harmonised classification (Repr. 2), which drives handling and labelling. Regulatory — EU REACH registration; EU CLP (2-ethylhexanoic acid Repr. 2)
Product emissions standards. The practical controls on bedroom foam are VOC-emission certifications: CertiPUR-US (for flexible PU foam) and GREENGUARD Gold set low-VOC limits that a tin-catalyst-heavy, high-emitting foam would struggle to meet, and California Section 01350 (CDPH) limits VOC emissions for products used in sensitive indoor settings. Industry — CertiPUR-US; GREENGUARD Gold; CDPH/California Section 01350 VOC-emission criteria
Where it is heading. The clearest signal is substitution: non-toxic bismuth catalysts now match or beat stannous octoate in flexible foam and are promoted as the greener replacement, and the industry is reducing tin loadings to cut VOCs — a market-led move ahead of any specific regulation. Peer-reviewed — El Khezraji et al. 2021 (bismuth catalyst replacing stannous octoate)
What the research says
- The classic flexible-foam gel catalyst. Sets the polyurethane network in mattress/cushion foam. Peer-reviewed — El Khezraji et al. 2021
- Persists as a residue. Tin and its acid by-product remain in cured, ageing foam. Peer-reviewed — Labouriau et al. 2006
- Cytotoxic in vitro. Toxic to fibroblasts and endothelial cells; among the more cytotoxic foam catalysts. Peer-reviewed — Tanzi et al. 1994
- A leading foam VOC source. Yields 2-ethylhexanoic acid, the main residual VOC after amines. Peer-reviewed — Rothe et al. 2001
What helps reduce it
Air out new foam. Let a new mattress or topper off-gas in a ventilated space; the acid VOC and other emissions decline with time. Peer-reviewed — Rothe et al. 2001 (VOC emission from new flexible foam)
Choose certified low-VOC foam. CertiPUR-US or GREENGUARD Gold foam is screened for low emissions, indirectly limiting tin-catalyst VOCs. Industry — CertiPUR-US; GREENGUARD Gold
Favour newer catalyst chemistry where disclosed. Bismuth-catalysed and reduced-tin foams are emerging and lower this specific source. Peer-reviewed — El Khezraji et al. 2021
What does NOT help
- Worrying about an old, aired mattress. The VOC emission is highest when new and falls over time; a years-old foam is well past its peak. Inferred
- Assuming "memory foam" is catalyst-free. Viscoelastic foams are still PU foams made with gel and amine catalysts. Inferred
Open research questions
- Real residual-tin levels in finished consumer mattress foam and any dermal transfer. Speculation
- The full bedroom-air contribution of 2-ethylhexanoic acid from new foam over a sleeper's first weeks. Speculation
- Whether bismuth and reduced-tin foams measurably lower indoor VOCs in practice. Speculation
Citations
- Rothe J, et al. (2001). New Catalysts for Low VOC in Flexible Slabstock Foam. J. Cell. Plast. After amine catalysts addressed, main remaining VOC is 2-ethylhexanoic acid from stannous octoate; cutting tin lowered total VOC. Via Consensus. Reference record Peer-reviewed
- Tanzi MC, et al. (1994). Cytotoxicity of some catalysts commonly used in the synthesis of copolymers for biomedical use. J. Mater. Sci. Mater. Med. Stannous octoate cytotoxic to fibroblasts and human endothelial cells. Via Consensus. Reference record Peer-reviewed
- El Khezraji S, et al. (2021). Use of Novel Non-Toxic Bismuth Catalyst for the Preparation of Flexible Polyurethane Foam. Polymers. Non-toxic bismuth catalyst as greener replacement for stannous octoate; higher isocyanate conversion. Via Consensus. Reference record Peer-reviewed
- Labouriau A, et al. (2006). Mössbauer and NMR characterization of tin octoate: neat and residues in foams. Polym. Degrad. Stab. Tin-octoate residues persist in cured foam; Sn(II)/Sn(IV) shift with age; acid by-product detectable. Via Consensus. Reference record Peer-reviewed
Frequently asked questions
What is stannous octoate?
Stannous octoate — tin(II) 2-ethylhexanoate — is the gel catalyst that makes flexible polyurethane foam set. When a mattress or cushion foam is poured, it is the tin catalyst that drives the reaction joining the polyol and isocyanate into the solid foam network. It is one of the two workhorse catalyst types in flexible foam, alongside the amine "blowing" catalysts, and it largely stays behind in the finished foam as a residue.
Why does it matter in the bedroom?
Two reasons. First, the tin catalyst doesn't fully leave: residues persist in cured foam, and the catalyst is cytotoxic in laboratory cell tests. Second, it degrades to 2-ethylhexanoic acid — and foam-industry research found that after amine catalysts are dealt with, this acid from the stannous octoate is the main remaining volatile organic compound off-gassing from flexible slabstock (bedding, furniture, carpet) foam. So a tin catalyst is both a residue in the foam you lie on and a source of the VOCs it emits.
Is it dangerous?
In context, the household exposure is low — this is a residue and a low-level VOC source, not an acute hazard. But it is not nothing: stannous octoate is cytotoxic in vitro, its 2-ethylhexanoic acid breakdown product is classified in the EU as a reproductive toxicant, and the foam industry itself treats the tin catalyst as something worth reducing or replacing. It is best understood as one of several reasons new foam off-gasses and a target for cleaner foam chemistry, rather than a reason to fear an existing mattress.
Are there safer alternatives?
Yes, and the industry is actively moving. Non-toxic bismuth catalysts have been shown to make flexible polyurethane foam with higher isocyanate conversion and better mechanical properties than stannous octoate, and they are promoted specifically as a greener, less toxic replacement. Foam makers are also reducing tin loadings to cut VOCs. For buyers, this is a case where "low-VOC," CertiPUR-US or GREENGUARD-certified foam, and newer catalyst chemistry all point the same way.
Related compounds
Embr is a sleep environment company researching and addressing the chemistry of the bedroom. Research and product development in progress. This page is informational and is not medical advice.
Last reviewed 2026-06-29. If you find a factual error, contact us.