Is TPU Toxic?

Have you heard of TPU? Your phone case may be made out of it. Or possibly it’s the film you ran through your 3D printer. That waterproof jacket you bought, made without PFAS? It could be a TPU coating on the fabric. 

As the abbreviation for thermoplastic polyurethane, TPU is a type of plastic (although some TPUs seem more like rubber.) It’s also a type of urethane, but very different from memory foam. 

No matter how you look at it, TPU is a petrochemical made out of fossil fuels. That fact alone makes it unhealthy. But just how toxic is TPU? Is it as toxic as the PVC it’s being used to replace?

In this article, find out everything you need to know about TPU. And since TPU is used in many different ways, there’s a lot to discover about its potential toxicity in each of them. With this information, you’ll be able to decide whether TPU is right for you and your family. If not, I’ll offer recommendations for TPU alternatives.

What is TPU?

TPUs, thermoplastic polyurethanes, are synthetic substances derived from fossil fuels. First developed in the 1950s, they are rapidly becoming PVC replacements. Here I briefly explain the chemical and physical characteristics of TPUs. To find out more about PVC, check out this article.

TPUs as Urethanes

Urethane is the general name for a large group of substances made from reactions between members of two chemical families: polyols and isocyanates. Polyurethanes are polymers made up of repeating units (monomers) joined by polyol-isocyanate (carbamate) links. 

Long and short polyols—which differ in the number of carbon atoms strung together—react with all kinds of isocyanates. Depending on the chemical combinations selected, their quantities, ratios, reaction times, and experimental conditions,  the resulting TPU product has a particular set of characteristics. With a specific end goal in mind, scientists custom create TPUs by tweaking the reactions used to make them.   

Polyols in TPUs

A polyol is the name for a large class of chemicals distinguished by two or more hydroxyl (-OH) groups. These groups are the locations of chemical actions with isocyanates during TPU creation. 

Examples of some of the many polyols used to make urethanes include glycerin (also in soap) or sorbitol (also in candy). Some TPU manufacturers marketing their products as green use plant oils as their polyol source. Most polyols, however, are made in the lab.

Long polyols are responsible for the elasticity of the TPU. Short polyols determine how tough and resistant to wear and tear the TPU is.

Isocyanates in TPUs

The other substance used to make TPU is an isocyanate. This chemical family is characterized by a carbon atom attached to both a nitrogen atom and an oxygen atom noted as N=C=O. In this notation, the capital letters represent the atoms of the three different elements. The lines between them stand for the attachments (bonds) between the atoms. 

It is at these locations in isocyanates where they react with polyols in TPU formation. To make TPU, diisocyanates with two of these groupings, or triisocyanates, with three of them, are used.

TPUs as Polyurethanes 

The characteristics of the final TPU products, such as whether they are stretchy, rigid, or foamy, depend on the particular polyols and isocyanates used in the reactions. It also depends on how strongly they are attached to each other. Various chemical additives to the urethanes, such as UV stabilizers or flame retardants, also partially determine these features.

TPUs as Thermoplastics

Thermoplastic substances are a type of plastic that will melt if exposed to high temperatures. Then they can be remolded to the same or different shape. Once solidified, they function as recycled plastic, usually with qualities inferior to the original substance. 

The reason thermoplastics melt easily is that they lack strong chemical cross links that hold them together. In thermoplastics, there are only looser, physical cross links. These links are reversible when heated at high temperatures. 

Can TPUs be Recycled?

Like some other thermoplastics you’re familiar with, such as polypropylene (plastic type #5) or polyethylene (plastic types #1, #2, or #4), thermoplastic urethanes (TPUs) can—in theory—be recycled. 

Unlike PVC (plastic type #3), TPUs do not need plasticizers, such as harmful phthalates, to be flexible. Nor is chlorine present in TPUs like it is in PVC, unless chlorine-containing additives are present. The fact that both plasticizers and chlorine are in PVC makes it difficult to recycle PVC.

What are the Three Main Types of TPU?

As discussed above, many different kinds of isocyanates and polyols can be combined to form a large number of TPUs. There are three general classes of TPUs depending on the starting materials used to form them. 

• Polyester TPUs: Possessing many high-performance characteristics (listed below), polyester TPUs work well when they’re blended with other thermoplastics. They are versatile TPU workhorses. Most TPUs fall into this class.
• Polyether TPUs: Especially resistant to microbes and water, polyether TPUs are great in waterproof applications.
• Polycaprolactone TPUs: Inherently tough like polyester TPUs, polycaprolactone TPUs perform well at low temperatures, and they resist breakdown by water. Very few TPUs of this class are used today.

What are the Physical Properties of TPUs?

There are many physical properties of TPUs that make them perform well in numerous products. Here are some of them.

• Resistant to abrasions and tears
• Elastic without losing its shape over a wide temperature range
• Able to withstand heat and cold
• Sunlight-resistant
• Can be transparent or be amenable to dyeing
• Impervious to chemicals including ozone and oxygen (so it won’t rust or degrade easily)
• Not affected by oil grease, gasoline, or chemical solvents

What Products Are TPUs In?

Because TPUs possess so many desirable physical characteristics, they are in many different kinds of products. Here is a partial list.

• Spandex
• Shoes
• Waterproof clothing
• 3D-printing film
• Toys 
• Medical devices (catheters, oxygen masks, tubing, dental retainers, etc.)
• Industrial equipment (cables, seals, films, filters, conveyor belts, etc.) 
• Electronics
• Sporting goods
• Automotive parts

What are the Health Effects of TPU?

TPU is generally considered non-toxic. Thus, it is commonly used in biomedical devices which may be inserted into patients. Here is an example of a scientific journal article showing TPU-PLA biomaterials used to build scaffolding for tissue or bone grafts as biocompatible. They do not result in cell death or genetic damage in experiments with human cell lines. 

However, another journal reference lists the chemicals used to make one type of TPU and an additive to it. They are not the safest ones available. In fact, they are quite toxic.

• 4,4′-methylenebis(phenyl isocyanate), also known as MDI. According to the U.S. Environmental Protection Agency (USEPA): “acute dermal contact with MDI has induced dermatitis and eczema in workers…Chronic (long-term) inhalation exposure to MDI has been shown to cause asthma, dyspnea, and other respiratory impairments in workers.”
• Poly(tetrahydrofuran), also called THF. Researchers showed how toxic THF is to environmental microorganisms. According to a safety data sheet on THF, it is a highly explosive and flammable suspected carcinogen. 
• 1,4-butanediol (BD). According to researchers, BD “rapidly converts to the date-rape drug gamma-hydroxybutyric acid (GHB) upon ingestion and resulted in the accidental poisoning of some children.” Sold illegally for bodybuilding, fat loss, and other reasons, BD is also sold as a fish tank cleaner or nail polish remover. This polyol is a central nervous system depressant.
• Quaternary ammonium salt. As I wrote in a previous article, this antimicrobial is so potent it leads to antibacterial resistance. It should be avoided when possible.

Admittedly, although there may be residual contamination of one or more of MDI, THF, or BD in a product made of a TPU, it is unlikely. The fact, however, that the manufacture of TPU exposes workers to these toxic chemicals—and makes a ready supply available for misuse—are reasons for not recommending TPU as a non-toxic plastic.

Is TPU in 3D-Printing Toxic?

Certain types of TPU are not only toxic, but they are also extremely hazardous when burned or heated to high temperatures, such as in 3D-printing. Some of the thermal breakdown products—some of which can be fatal if inhaled—include:

• Hydrogen cyanide
• Carbon monoxide
• 4,4′-methylenebis(phenyl isocyanate) 

Nitrous oxides (NO_x), the harmful air pollutants common in car exhaust and from power plants, are also thermal decomposition products when TPUs are heated at high temperatures.

Fine dust given off during the use of TPU filament can also present a danger to health. (So don’t allow it to accumulate on surfaces because it could form an explosive mixture.)

To the best of our knowledge, all 3D-printing filaments are plastic—usually polylactic acid (PLA). This is reason enough for us to consider not using 3D-printing. If you wish to lessen your environmental impact from 3D-printing, you may want to choose 100% recycled filament.  

Is TPU Food-Safe?

According to the U.S. Food and Drug Administration (FDA), some polyurethane resins are considered safe for dry food contact. For example, TPUs are common as conveyor belt materials used to move dry food from place to place on a farm, mill, or factory. However, a thorough search of the FDA database found no evidence of FDA approval for TPUs in wet food contact. 

So, using a TPU bowl or plate—such as the one you made with TPU filament on your 3D printer—to hold prepared food is, unfortunately, not something I can endorse. 

A list of approved isocyanates and polyols to make TPU is available in the Code of Federal Regulations. What is concerning is that a few isocyanates are molecules containing benzene or toluene parts. Benzene is a known carcinogen. Toluene is a known teratogen.

Note: Benzene and toluene are not in TPU, but molecules similar to them are. One of them, bis(isocyanatomethyl) benzene, is moderately toxic by ingestion. It is characterized as a severe skin and eye irritant as well as a flammable liquid. If decomposed by heat, this chemical emits toxic fumes of NO_x, a common component of car exhaust. Additionally, there could be residual benzene or toluene present as contaminants.

The FDA also permits the use of several additives in TPUs. Some of these are chemicals containing polyvinyl, and others contain chloride. Note: This doesn’t mean toxic polyvinyl chloride is in TPUs, but the substances needed to form it may be present in TPUs with those particular additives. 

Unfortunately, as a consumer, there is no way to know or find out. If asked, companies will claim it’s proprietary information. They are not legally required to reveal the components used in their TPU products. 

Incidentally, the presence of chlorine in some TPUs complicates its recycling. It is a reason why TPU should not be called recyclable (for the same reason PVC should not be referred to as recyclable, either).

Is TPU Safe for Skin?

Generally under ambient conditions, TPUs are safe for skin. It’s always advised to check the safety data sheet of the particular TPU you’re considering touching to see if there’s any warning about dermal contact.

Endocrine disruptors, such as BPA or phthalates, are not typically present in TPUs. They are flexible by nature so need no plasticizers to make them so. 

(Touching products containing BPA or phthalates—such as store receipts or flexible plastic toys—is not a good idea. Those chemicals are easily absorbed upon skin contact.)

Is TPU Material Safe for Babies?

It appears that TPUs may be safe for babies for some uses. For example, TPUs most likely do not contain endocrine disruptors such as phthalates because they are flexible already. BPA, another endocrine disruptor, is used to make polycarbonate plastic. BPA is not listed by TPU manufacturers as an additive to their products. So, placing your newborn baby on a TPU floor mat may be safe.

However, if your baby can grab and chew things, it is not prudent to have products made with TPU in their reach. As discussed in this article, there is always the possibility of residual toxic chemicals in TPUs.

Similarly, TPU does not appear to be FDA-approved for wet food contact. So giving food to your baby on a plate or bowl made with 3D-printed TPU filament is not advised.

TPU vs PVC (Is TPU better than PVC?)

While it’s true that TPU is safer than PVC, this does not mean TPU is safe, as I’ve explained above.

In a previous article, I did a full investigation into PVC from cradle to grave. My findings reveal the full extent of the toxicity of this plastic. So, saying that TPU is safer than PVC is not giving TPU an enthusiastic seal of approval. 

Some of the common chemicals used to make TPU are hazardous to work around, so individuals exposed in a workplace setting may suffer more harm than regular consumers using everyday goods made from TPU.

TPU Alternatives

There are so many different kinds of TPUs used in a plethora of diverse products that a complete list of TPU alternatives is impossible. Here are a few suggestions for common products.

1. Bio-based phone case
2. Stainless steel and/or glass food storage containers
3. Wooden toys
4. Leggings & activewear with little to no spandex
5. Natural shoes

Is TPU Toxic? Final Thoughts

Filling the materials gap between rubber and steel, TPUs are unlike other plastics because they have impressive portfolios of varying characteristics that meet most requirements. They are commonly used in the biomedical, electronics, sporting goods, and automotive industries. Certain forms of TPU are FDA-approved for dry food contact.

TPU manufacturers claim their product is non-toxic. It is true that TPU is less toxic than polyvinyl chloride (PVC), but it is not as non-toxic as you would have hoped for. 

The greatest toxicity risk occurs when TPU is used as 3D-printing film. Toxic fumes upon heating are harmful to health.

As a fossil fuel-derived chemical, TPUs will never completely biodegrade. They may be recycled and made into lower-quality goods, but they rarely are. The reason is the lack of appropriate facilities. It’s much cheaper to make TPUs from virgin materials. Most used TPUs are landfilled or incinerated.