NBR foam (Nitrile Butadiene Rubber foam) is a synthetic elastomer widely used in consumer products, from yoga mats to pipe insulation. While the material is stable and generally considered safe once fully cured, concerns about toxicity arise from the chemicals involved in its creation. The initial manufacturing and off-gassing process involves the temporary release of specific chemical compounds that warrant attention.
What NBR Foam Is Made Of
Nitrile Butadiene Rubber is a copolymer built from two different monomer units: acrylonitrile and butadiene. The finished NBR polymer is valued for its superior resistance to oils, fuels, and abrasion. This stable, long-chain polymer forms the bulk of the finished foam product.
Toxicity concerns typically stem not from the finished polymer, but from the various additives and unreacted components used during manufacturing. NBR foam production requires the addition of vulcanizing agents, accelerators, plasticizers, stabilizers, and foaming agents to achieve its soft, flexible, and cellular structure. A common plasticizer used to enhance flexibility is dioctyl phthalate (DOP), though its use is often restricted in consumer goods due to health concerns.
Residual amounts of the original monomers, acrylonitrile and butadiene, may remain trapped within the foam cells after the foaming process. Manufacturers must carefully control the curing and foaming steps to ensure that these unreacted monomers are minimized. The final product is a complex blend, where the stable rubber matrix encapsulates trace amounts of these manufacturing aids.
Volatile Organic Compounds and Off-Gassing
The primary safety concern with new NBR foam products is off-gassing, which is the release of volatile organic compounds (VOCs) into the surrounding air. VOCs are carbon-based chemicals that easily vaporize at room temperature, and they are responsible for the distinct “new product” smell associated with fresh foam. This release is highest when the product is first unwrapped and begins to cure fully.
The specific VOCs of concern in NBR foam include residual monomers like butadiene, classified as a human carcinogen, and acrylonitrile, a probable human carcinogen. Trace amounts can persist and off-gas, even though the bulk of these are consumed in the polymerization process. Other VOCs may originate from unreacted processing aids, solvents, or the breakdown products of foaming agents.
Exposure to high concentrations of these VOCs in a poorly ventilated space can cause immediate, temporary symptoms, including irritation of the eyes, nose, and throat, headaches, or dizziness. To mitigate this initial exposure, air out the new NBR foam product, such as a yoga mat, outdoors or in a well-ventilated area for several days before regular use.
Regulatory Oversight and Consumer Safety Measures
The long-term safety of NBR foam in consumer products is managed through global regulatory standards designed to limit the content of hazardous substances. Regulatory bodies enforce limits on specific heavy metals and certain phthalates, like DOP, used as plasticizers. Compliance with these established safety thresholds helps assure that the chronic risk from a cured product is very low.
Consumers can look for certifications that indicate a product has met rigorous third-party testing for chemical emissions and content. For instance, compliance with the European Union’s Restriction of Hazardous Substances (RoHS) directive confirms the foam does not contain excessive levels of specific restricted materials, including lead, mercury, and certain phthalates. Similarly, the Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH) regulation restricts the use of Substances of Very High Concern (SVHCs) in products sold in the EU.
These measures ensure that the residual chemicals in the finished product are kept below levels considered harmful for continuous exposure. Manufacturers who adhere to these standards provide an additional layer of assurance regarding the material’s safety beyond the initial off-gassing period.