Formaldehyde is an organic chemical with the formula HCHO, a molecular weight of 30.03, and is colorless and odorless in its gaseous state. This notorious small-molecule gas compound never fails to attract attention. On October 27, 2017, a list published by the World Health Organization’s International Agency for Research on Cancer included formaldehyde as a Class I carcinogen. Formaldehyde’s acute toxicity irritates the skin and mucous membranes. Long-term retention in formaldehyde can diminish respiratory function, cause irreversible damage to the nervous, digestive, and cardiovascular systems and various organs. So, how did such a terrible chemical find its way into flooring? And how can we be sure that the flooring we choose is safe and harmless?

Molecular model of formaldehyde

The author has studied wood science in college for seven years, worked in testing laboratories for more than four years with hundreds of formaldehyde emission testing experiences. This article may touch on some controversial views. If they run counter to your previous understanding of the topic, this article will take precedence.

Formaldehyde Emission Test

In-Depth Description

  • Where does Formaldehyde Come From?

Wood products rely on a plethora of adhesives. In ancient times, our ancestors used glues extracted from the skin and bones of animals. Although eco-friendly, these prehistoric alternatives have disadvantages that make them unsuitable for application in the modern wood industry—most notably low yield, low bonding strength, and poor weather resistance. 

In today’s wood industry, popular adhesives such as urea-formaldehyde resin (UF), melamine-modified urea-formaldehyde resin (MUF), and phenolic resin (PF) all have formaldehyde as the main synthetic raw material. Since these addition reactions (in other words, organic chemical reactions where two or more molecules combine to form a larger one) are reversible—in the case of UF resins, for example, the reaction is always incomplete when UF resins are synthesized by urea and formaldehyde with moderate catalyst, the large-molecule UF resins and small-molecule substances like urea and formaldehyde exist together in the final product. It even keeps decomposing after cured. Thus free formaldehyde is always in the adhesive system, and wood-based panels produced with UF resins will release formaldehyde for years or even decades to come. The reversible addition reaction equation and the reactors for UF resin production in the factory are illustrated as below.

n H2N-CO-NH2 + n HCHO ⇌ H-[NH-CO-NH-CH2]-OH + (n-1) H2O

Reaction still

Formaldehyde emissions from MUF and PF resins are much lower. Nowadays, wooden panel and flooring production utilizes low-formaldehyde adhesives, such as resorcinol phenol-formaldehyde resin (RPF), methylene diphenyl diisocyanate resin (MDI), and polyurethane resin. It’s good to know you can now choose specific flooring made with these low toxicity, formaldehyde-free adhesives.

  • Standard, Test, and Certification

The three main methods to test flooring for formaldehyde emissions are the desiccator method, perforation method, and climate chamber method. Each has its advantages and disadvantages (the author will discuss these in a future article).

The main certification for formaldehyde emissions includes CARB, JAS, CE, etc. Markets in different regions are subject to different types of certification. As with the product testing standards, the limitations on formaldehyde emissions are also stated differently. The Japanese Ministry of Agriculture, Forestry, and Fisheries (JAS) certification, for instance, is one of the strictest. The test uses the desiccator method, following Japanese agricultural standard JAS 1073, under which formaldehyde emissions are ranked into F☆☆☆☆, F☆☆☆, and F☆☆. To qualify the highest grade F☆☆☆☆, the average formaldehyde emission value should be no larger than 0.3 mg/L, and the maximum value should be no more than 0.4 mg/L. The testing specimen and desiccators used for collecting formaldehyde are illustrated as below.

JAS 1073 Test samples
Desiccator method in JAS standard

Some subversive points you should know

  • 1 What you smell is not formaldehyde!

Once again, formaldehyde in gaseous form is colorless and odorless. In the laboratory, formaldehyde standard high-concentration solution (showed as below) is often used in the test. Little odor can be sensed when opening the ampoule bottle. But odorless isn’t equal to non-irritating. These invisible water-like chemical reagents need to be more vigilant. Protection throughout is essential.

Formaldehyde standard high-concentration solution

When working with the flooring, you may have encountered the strong smell of something like paint or glue or other unpleasant-smelling substance. These are Total Volatile Organic Compounds (tVOC), a series of gaseous compounds, including toluene, xylene, and others, which, just like formaldehyde, pollute indoor air quality. They are extremely common in flooring, furniture, wall coatings, and other standard household items. So, even if you buy a product with qualified formaldehyde emission, you cannot be sure that the indoor atmosphere will be completely safe as there are many potential sources of pollution in your room. If you are still worried about indoor air pollution, find a reliable agency to test for the presence of formaldehyde and tVOC in your room. 

  • 2 Methods for removing formaldehyde

This is the most frequent question I have been asked in my career. You may have heard of chemical formaldehyde remover, high-temperature ventilation, green-plant and activated-carbon adsorption, air purifiers, and other methods. They may be effective, but not once and for all.

As mentioned earlier, the addition reaction of adhesives is reversible, so formaldehyde will be released all the time. Formaldehyde removal methods may only reduce the concentration in the room for a short time, but the continued release of the chemical is inevitable. Therefore, my advice is, don’t waste money fighting with formaldehyde, buy better quality flooring in the first place.

  • 3 Zero Formaldehyde? I wouldn’t say so.

Strictly speaking, all we can say with certainty is that the concentration of formaldehyde is below the detection limit. Wood is an organic material composed of chemical components such as cellulose, hemicellulose, and lignin that nature slowly degrades into small molecules under conditions in which formaldehyde plays a natural role. In addition, clothes, car interiors, and a variety of day-to-day necessities also release formaldehyde. Hence, there is no need to be terrified at the mention of formaldehyde—below the limitation, the compound is harmless.

In addition, formaldehyde emanating from flooring using EPI, PF, and even soybean glue as adhesives could be so low as to be considered non-existent.

MDI and PF resin used in engineered flooring
  • 4 Which kind of flooring should I choose?

When asked which types of wooden panels emit the most formaldehyde, professional teachers in college would reel off the following list, from high to low: fiberboard, particleboard, plywood, and solid wood. However, my years of working in the testing lab convinced me that the teachers’ answer was only a general rule and can vary due to the different amounts and types of adhesive used.

Currently, a three-layer solid wood core flooring with a middle core layer of solid wood slats perpendicular to the surface seems to have achieved low formaldehyde status because it combines a larger than average solid wood component with less adhesive. But this should not be taken for granted. Many three-layer floorboards use fast-growing wood like poplar or eucalyptus as core layer slats. Compared to an entire hardwood board or a plywood core, there are usually some defects like knots, chipped edge, and insufficient width on the slats that call for more adhesive for filling cracks or gaps in order to prevent rib-like dents on the top lamella. In my testing-lab days, I occasionally encountered test results that shocked me and our clients. Therefore, regardless of the type of flooring, my advice is, find a certificated third-party laboratory and get your flooring tested. 


1. Undoubtedly, formaldehyde is so harmful that no one should ever ignore it. But in my years of lab experience, it was clear that the quality of wooden products was indeed getting better and better.

2. Product testing does have certain limitations. The tests focus solely on product quality during manufacturing and distribution. And the tests strictly follow the sampling prescription in a certain proportion given in the standard. All test reports contain the disclaimer that the test results are only responsible for the received sample. The actual air quality in the room needs further testing. Furthermore, formaldehyde emissions are not the only quality index we should consider when selecting flooring. The tVOC is also worthy of attention.

3. If you encounter controversial flooring products, commission qualified third-party laboratories to conduct formaldehyde emission tests.

4. Choosing a certificated flooring brand or manufacturer is always the sensible option. The certificate authorities have strict quality requirements and regularly sample the manufacturers’ products for inspection.

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