At a glance
| Chemical family | Epoxide (methyloxirane) — a small reactive cyclic ether; the principal polyether-polyol feedstock |
| CAS number | 75-56-9 |
| Classification | IARC Group 2B (possibly carcinogenic to humans), Monograph Volume 60 (1994); NTP — reasonably anticipated to be a human carcinogen; eye and respiratory irritant |
| Where you encounter it | Chemical manufacturing — roughly 58% of US propylene oxide makes polyurethane polyols, the rest mostly propylene glycol and glycol ethers; also a historical fumigant |
| Sleep micro-environment relevance | The principal feedstock for the polyol half of polyurethane foam; consumed in making the polyol, so not a documented emission from finished mattress foam |
| Activated carbon capture | Limited — a small, volatile, reactive epoxide; not a primary capture target, and not emitting from finished foam |
What it is
Propylene oxide is an epoxide — like ethylene oxide but with a methyl group — and shares the ring-strain reactivity that makes epoxides such useful building blocks. Its single largest job is feedstock chemistry: reacted (polymerized) to build polyether polyols. In the United States, about 58% of propylene oxide goes into polyurethane polyols, with most of the remainder making propylene glycol and glycol ethers. When people talk about "the polyol" in polyurethane, propylene oxide is usually where it started.
IARC classifies propylene oxide as Group 2B — possibly carcinogenic to humans — on the basis of sufficient evidence in experimental animals and inadequate evidence in humans; the available human studies were confounded because the workers were also exposed to ethylene oxide. Peer-reviewed — IARC Monograph 60 The U.S. National Toxicology Program lists it as reasonably anticipated to be a human carcinogen, and it is an eye and respiratory irritant. Regulatory — NTP, EPA
How it relates to the bedroom
The polyol half of your mattress foam
Polyurethane is the reaction product of an isocyanate and a polyol. The isocyanate side is TDI or MDI; the polyol side is, overwhelmingly, built from propylene oxide. So propylene oxide is one of the two fundamental chemical origins of the foam — the part that, in flexible foam, gives the polymer its soft, resilient character. Understanding propylene oxide is understanding where the "give" in a foam mattress comes from chemically. Regulatory — EPA polyether polyols
Consumed upstream, not a finished-foam emission
Like ethylene oxide, propylene oxide is reacted away long before the foam reaches a mattress. The reactive epoxide is opened and incorporated into the polyol chain during polyol manufacture; the polyol then reacts with the isocyanate to cure the foam. A finished mattress is not a documented propylene-oxide source. Inferred — propylene oxide is consumed in polyol manufacture; finished foam is not a characterised source
Where exposure actually occurs
The documented propylene-oxide exposures are occupational — in the plants that make and react it — and it has historically been used as a fumigant. Consumers are not meaningfully exposed to propylene oxide from the downstream products (polyols, polyurethane, propylene glycol), because the reactive epoxide has been consumed. Regulatory — EPA hazard summary
What the research says
Carcinogenicity
The Group 2B classification rests on clear animal evidence with human evidence judged inadequate (confounded by ethylene-oxide co-exposure). Peer-reviewed — IARC Monograph 60 As a reactive epoxide it is directly alkylating, the same general mechanism that underlies its sibling ethylene oxide's stronger classification — but the human data for propylene oxide specifically remain limited.
The honest bedroom position
Propylene oxide earns its place in the Atlas as the chemical origin of the polyol — half of what a polyurethane mattress is made from. It does not earn a place as a finished-foam exposure, because it is consumed upstream. Naming it completes the foam-chemistry picture without implying your mattress emits it. Inferred
What helps reduce exposure
This is upstream chemistry, not a consumer exposure to manage. Propylene-oxide control is occupational and regulatory — in the chemical plants that produce and react it. There is no meaningful finished-mattress propylene-oxide exposure to reduce.
Material choice still applies for the broader picture. Choosing non-polyurethane mattress constructions (natural latex, innerspring with natural-fiber layers) avoids the whole isocyanate-and-polyol system — relevant to foam off-gassing generally, not to propylene oxide specifically, which is already consumed.
What does NOT help
- Treating finished foam as a propylene-oxide source. It is consumed in making the polyol; the cured mattress does not emit it.
- Confusing propylene oxide with propylene glycol. Propylene glycol (a common, low-toxicity humectant) is a downstream product; it is a different compound with a very different safety profile.
- Air filtration as a propylene-oxide fix. There is no finished-mattress emission to filter.
Open research questions
- Whether any trace unreacted propylene oxide persists into finished polyol or foam under real manufacturing conditions. Speculation
- The relative contribution of polyol-side versus isocyanate-side residuals to total new-foam emissions. Speculation
Citations
- IARC Monographs Volume 60 (1994). Propylene oxide — Group 2B (possibly carcinogenic to humans). Peer-reviewed
- NTP. 15th Report on Carcinogens — Propylene oxide (reasonably anticipated to be a human carcinogen). Regulatory
- EPA. Propylene oxide (75-56-9) Hazard Summary. Regulatory
- EPA. Polyether Polyols Production NESHAP — propylene oxide as the principal polyol feedstock. Regulatory
Frequently asked questions
What is propylene oxide used for?
Most propylene oxide — around 58% in the US — is used to make polyether polyols, the polyol component that reacts with isocyanates to form polyurethane foam. The rest goes mainly to propylene glycol and glycol ethers. So propylene oxide is, more than any other single chemical, the feedstock for the polyol half of your mattress foam.
Is propylene oxide a carcinogen?
IARC classifies propylene oxide as Group 2B — possibly carcinogenic to humans — based on sufficient evidence in animals and inadequate evidence in humans (the human studies were confounded by co-exposure to ethylene oxide). The U.S. National Toxicology Program lists it as reasonably anticipated to be a human carcinogen. It is also an eye and respiratory irritant.
Is propylene oxide in my mattress?
Not in any significant amount. Propylene oxide is consumed upstream when it is reacted to build the polyol; the polyol then reacts with the isocyanate to form the cured foam. By the time foam is in a mattress, the propylene oxide is long since reacted away. It belongs in the foam-chemistry story as the polyol feedstock, not as a finished-mattress emission.
Where does propylene oxide exposure happen?
The documented exposures are occupational — in chemical manufacturing where propylene oxide is produced and reacted. It has also been used as a fumigant. For consumers, finished products made downstream of propylene oxide (polyols, polyurethane, propylene glycol) are not propylene-oxide sources, because the reactive epoxide has been consumed.
How is propylene oxide different from ethylene oxide?
They are sibling epoxides. Ethylene oxide is the IARC Group 1 known human carcinogen used heavily as a sterilant; propylene oxide is IARC Group 2B (possibly carcinogenic) and is the larger feedstock specifically for polyurethane polyols. Both are reactive epoxides consumed upstream of finished foam.
Related compounds
Embr is a sleep environment company researching and addressing the chemistry of the bedroom. Research and product development in progress.
Last reviewed 2026-06-27. If you find a factual error, contact us.