Wood Guide

Wood Information

What is “wood” with quotation marks?

This is how I describe wood-like products that contain a mixture of wood, resins, and plastics. It covers engineered wood, plywood, MDF, particleboard, composite wood, OSB, and others.

What is engineered wood?

Engineered wood consists of thin pieces of solid wood attached with glue to either side of a non- solid wood core. The core can be either plywood or ground wood fibers mixed with resin— basically a glue. The outer solid wood surface is called a veneer. The glue holding the veneers onto the core, and the glue-based binders in the core, are where the health issues potentially lie, since these glues typically contain urea-formaldehyde, a carcinogen and airway irritant.

Happily, some of the newer engineered wood uses bio-based or formaldehyde-free glues that are much healthier than the old engineered woods.

Engineered wood is often used in furniture construction, like in making couches, because it is even stronger than solid wood and can hold up to many years of wear and tear.

What is engineered hardwood? Is it different than regular engineered wood?

No, it’s the same thing. My guess is that this phrasing is a marketing term used to make the product seem a little more like it’s true hardwood.

Is engineered wood toxic?

It depends entirely on what the glue/resin/binder is that holds the wood together. If it is held together with a soy-based resin with no added formaldehyde, for example, then it’s a healthy option. If it is held together with a glue that contains formaldehyde, or a glue that contains other harmful chemicals like isocyanates, then it is harmful to health.

What is plywood?

Plywood is made of many layers of super-thin pieces of solid wood. Each layer’s grain is stacked perpendicular to the one above and below it, and all the layers are attached with an adhesive binder (plywood can have up to 3.5% binder by weight). Alternating the wood grain at perpendicular angles makes plywood even stronger than wood, and is why you see it used for home construction. After the layers are glued together, heat and pressure are applied to make a smooth plywood panel.

Like engineered wood, there are newer, healthier versions of plywood that are made with formaldehyde-free, soy-based resins instead of standard glues. PureBond is an example of a brand that is doing this.

What is composite wood?

Composite wood is very similar to engineered wood, but the materials in the core aren’t always wood-based. Instead, it is often a blend of plastics and wood.

What is MDF?

MDF means medium-density fiberboard and it is made with wood pulp mixed with a resin binder (with up to 10% by weight) to make a wood-like product. This is what IKEA uses in their cupboards, for example, then covers them with a layer of laminate.

What is particleboard?

Particleboard is a type of composite wood made with wood chips mixed with a binder (up to 12% by weight) to make a wood-like product. This is what IKEA uses in its KALLAX furniture, for example.

Does all wood have formaldehyde in it?

Yes, trees emit 9ppb (parts per billion) of formaldehyde, so all wood contains some naturally. This is why the term “no added formaldehyde” or NAF is preferred for “wood” products— it’s more technically correct. For reference, the laws passed in 2010 that regulate added formaldehyde-based resins in plywood, particleboard, and MDF limit the formaldehyde emissions to 90ppb.

What is NAF engineered wood (and ULEF?)

NAF stands for “No Added Formaldehyde.” This means the binders used to glue the wood together don’t contain urea-formaldehyde.

ULEF means Ultra-Low Emitting Formaldehyde, and may be achieved by adding a chemical that sequesters, or captures, formaldehyde from escaping. These are called Formaldehyde Scavengers. It may also mean there is a blend of formaldehyde and non-formaldehyde based binders.

Composite wood that is “CARB or TSCA compliant” means that it has low formaldehyde levels, but not ultra-low. Since 2019, all plywood, MDF, and particleboard manufactured or imported into the US must be compliant.

What are other types of engineered and composite wood?

Oriented Strand Board (OSB), Hardboard, Laminated Veneer Lumber, Glulam, and other wood-type products are some of the other types of engineered wood (and there are a lot!) These are a little different than plywood, MDF, and particleboard for two main reasons: one, they’re not regulated by the EPA to ensure that they contain low levels of formaldehyde, so may have higher levels of harmful off-gassing. Second, they’re less common in furniture, which of course, Interior Medicine focuses on, so that’s all I have to say about them!

What is fake wood flooring made of?

It’s usually either laminate or LVP, luxury vinyl plank. Laminate flooring can have some wood in its core, or be 100% plastic, depending on the brand. The top layer is a piece of fiberboard with a photo of wood laminated to the top, then covered in a wear-resistant coating. This coating can be scratch-resistant, or water-resistant (which often means it contains PFAS). LVP is 0% wood and is made with vinyl, widely regarded as the least sustainable and least healthy choice of plastic flooring available. Some brands have phthalates and harmful recycled content added to it. Some brands are coated in PFAS to make them more wear and water resistant.

Is bamboo solid wood?

Sometimes! Bamboo is technically a grass, and can be solid, or more like engineered wood, when used in home products. Solid bamboo is rarely, but sometimes used as flooring. More often, like you see in butcher blocks or cutting boards, bamboo is processed in a vertical or horizontal fashion, a lot like plywood— thin strips of bamboo are glued and compressed together to make a strong, solid board. Or, bamboo veneers are glued to cores made with a variety of materials, depending on the brand.

What are “the worst additives” added to fake woods?

These are PFAS, BPA, antimicrobials, and heavy metals. These are most commonly mixed in with luxury vinyl flooring. (FYI, I follow Green Science Policy’s “6 worst” chemical classes to avoid.)

Are wood stains toxic?

Wood stains are often, but not always, toxic to health. It depends completely on the kind you use. A completely natural wood stain like coffee is obviously safe. Water-based wood stains are relatively non-toxic, especially ones with certifications like GreenSeal-11 ensuring the most harmful additives are avoided. Ones without VOCs, antimicrobials, chemical drying agents, or heavy metals are a better choice. Oil-based wood stains with standard chemicals that release high VOCs are quite harmful to health.

What is a 100% natural wood stain?

While I don’t know of any that come in a purchasable can, people do use coffee grounds, tea, walnut husks, and other natural materials to stain wood. Since these are generally less permanent, they require a finish on top to seal them in.

What is the difference between wood stain and wood finish?

Wood stains add color to natural wood, while a finish protects it.

Why are oil-based finishes, but water-based stains, better?

Natural, oil-based finishes like linseed oil, hemp oil, or tung oil are minimally processed, and very low in VOCs. Water-based finishes often contain high-VOC, toxic solvents to make them work better. On the other hand, natural, oil-based stains typically have higher VOCs, whereas their water-based counterparts, have less.

What are plant-based oil finishes?

Linseed, hemp, and tung oil are types of plant-based oil finishes. Linseed oil comes from the flax plant. Hemp oil comes from the cannabis plant. Tung oil comes from the Tung tree (Vernicia fordii), native to China, Myanmar, and North Vietnam.

What are solvent-based finishes?

Varnish, acrylic, synthetic lacquer, and urethane-based finishes all require a much higher solvent concentration than water-based finishes, so are quite high in VOCs that irritate your respiratory tract and can cause other issues. They also often contain carcinogenic chemicals.

Is shellac toxic?

It depends if you’re talking about natural shellac or synthetic shellac. Natural shellac comes from the cocoon-like secretions of the female lac bug, and has been used for thousands of years. Synthetic shellac contains solvents, and has a harmful vapor.

What is FSC certified wood?

FSC, or the Forest Stewardship Council certification, is focused on responsible management of forests. For wood, it means that the trees it comes from meet forest management standards, indigenous people’s rights are respected when harvesting, and old growth forests are not disturbed. It’s a fantastic certification in terms of our environment and community, but FSC-certified wood can still be treated or finished with many other chemicals that harm your health.