Would you believe that your memory foam pillow is made out of the same chemicals as some types of 3D-printer filament? It’s true.
That’s just one of many interesting facts about a large chemical family called the polyurethanes (PU). Thermoplastic polyurethanes (TPU) are some of the newest members of that family.
In this article, you’ll learn the major differences between PU vs. TPU. Here we’ll cover:
- Toxicity and safety concerns
- Environmental impacts
- Recyclability
- Which types of products you’re more likely to find each one
(By the way, this article is meant to be a comparison of the two types of material. For a closer look at PUs, check out this article. And for a deep dive into TPUs, check out our piece here.)
Table of Contents
The Chemistry of PU vs. TPU
Remarkably, the same types of chemicals are used to make both polyurethanes (PU) and thermoplastic polyurethanes (TPU). Polyols and isocyanates are joined by urethane (carbamate) linkages in a repeating and alternating fashion to form urethane polymers.
Scientists tweak many variables to produce urethanes with desired properties. The major variables include:
- Specific polyols and isocyanates
- Ratio of polyols to isocyanates
- Reaction conditions (catalyst, length of reaction, temperature, pH, etc.)
- Additives used (flame retardants, UV stabilizers, antimicrobials, plasticizers, etc.)
Thermoset vs. Thermoplastic Polyurethanes
There are two broad categories of polyurethanes. They can be either thermoset or thermoplastic. Memory foam is an example of a thermoset. TPU is a thermoplastic. A key difference between them depends on how they react to heat.
Thermoset Urethanes
Thermoset urethanes are plastics that get their name from the fact that they are set once formed and will not melt if subjected to heat. (They will burn or char, however.) So, thermosets are not easily recyclable as plastics that will melt, be remolded, then solidify into a downcycled product.
The strong chemical cross linkages between and among the repeating units of polyols and isocyanates in a thermoset urethane mean they will not break apart under high heat. In other words, these chemical linkages are not reversible.
Thermoplastic Urethanes
By contrast, thermoplastic urethanes will melt if exposed to high temperatures. Then they can be remolded to the same or different shape.
The reason they melt easily is that they lack the strong chemical cross-links that thermosets have. In thermoplastics, there are only physical cross-links that are reversible when heated. Weak hydrogen bonds between chains are present, but easily broken by heat.
Here’s a schematic that illustrates the crosslinking difference:
Like some other thermoplastics such as polypropylene (plastic type #4) or polyethylene (plastic type #1 or #2), thermoplastic urethanes (TPU) can—in theory—be recycled.
Unlike polyvinyl chloride (PVC), some TPUs are naturally flexible and do not need added plasticizers, such as harmful phthalates, to be flexible. (PUs do need plasticizers for some uses, such as artificial leather.) Nor do TPUs contain chlorine, which would complicate their recyclability as it does with PVC.
Incidentally, one similarity between thermosets and thermoplastics is that they both can be elastomers (elastic polymers). These substances return to their original shape if stretched, sometimes with additives to make them more elastic. Memory foam is a perfect example.
Characteristic Differences Between PU vs. TPU
Both polyurethanes (PU) and thermoplastic polyurethanes (TPU) can possess nearly the same characteristics. It depends on their chemical components and the other factors listed above. However, there are some key differences presented in the table below that apply to most PUs and TPUs.
| Property | Thermoset PU | Thermoplastic PU (TPU) |
| Abrasion resistance | High | Low (may tear) |
| Heat resistance | Burns or chars above 480℉ | Melts at 365℉ |
| Hardness | Maximal | Minimal |
| Load bearing capacity | High | Low |
Toxicity Differences Between PU vs. TPU
Unfortunately, it’s inaccurate to say TPUs are less toxic than PUs as a generality. After surveying many urethane manufacturers, I found company cases where brominated flame retardants, phthalate plasticizers, or fluorinated blowing agents were added to TPUs, often referred to as the more eco-friendly urethane. All three of those additives would nullify any claim to environmental friendliness.
However, some TPU products may be relatively eco-friendly. For example, many TPUs are inherently flexible, so they probably wouldn’t contain added phthalate plasticizers. But in PU leather, they would definitely be present.
Similarly, since TPU is frequently touted as biocompatible, implantable TPU devices most likely do not contain plasticizers or flame retardants. But it’s a good idea to ask before surgery.
As another example, ozone layer-destroying greenhouse gases (fluorinated substances) serving as blowing agents would probably not be in non-foam urethane products, including both PUs and TPUs.
Keep in mind that all urethanes—PUs and TPUs—contain isocyanates. Many of them are quite toxic to workers exposed to them on a daily basis. Average shoppers would never have the same exposure. However, there could be residual levels of contaminants that could pose health problems if breathed in or touched. There are reports of that happening.
To be safe, ask the product’s manufacturer about the presence of phthalates, flame retardants, or antimicrobials. Each of these carry their own risks. Request the specific names of these additives as well as the isocyanates used.
I suspect companies will claim all that is proprietary information. If you’re able to get a chemical name, research its toxicity. If you can’t find out anything from a manufacturer, you’ll have to decide whether an alternative product listed in our articles on PU and TPU may be better for you and your family.
Pros & Cons of PU vs. TPU
Because there are so many different polyurethanes and thermoplastic polyurethanes, it is not possible to clearly distinguish pros from cons. So, our table serves as a general guide to PU vs. TPU.
| Factor | PU | TPU |
| Cost | $2.77/lb. | $2.50/lb. |
| Toxicity | Moderate to high | Low to moderate |
| Sustainability | No (fossil fuel) | No (fossil fuel) |
| Biodegradability | No | No |
| Recyclability | Low | Low |
Final Thoughts on PU vs. TPU
Polyurethanes (PU) and thermoplastic polyurethanes (TPU) are chemically similar. They are both made from fossil fuel-derived polyols and isocyanates, making them plastics.
Some of the reasons the same starting materials can result in products with significantly different characteristics include:
- Polyol-isocyanate combinations vary
- Crosslinks may be physical or chemical, extensive or minimal
- Reaction conditions (catalysts, temperature, pH, etc.) differ
- Additives (plasticizers, UV stabilizers, etc.) change
You can find both PUs and TPUs in most of the same consumer products ranging from household goods to electronics to automotive. TPUs are becoming the preferred material in implantable medical devices because of their biocompatibility. PUs have been the standard in foam products (pillows, mattresses, furniture) and home insulation since the 1950s.
In terms of toxicity, both PUs and TPUs are made with diisocyanates which are hazardous to workers, leading to respiratory illnesses. Some diisocyanates are carcinogenic in lab animals. Several PBDE flame retardants added to polyurethane foam products or artificial leather are extremely toxic.
TPUs are more likely to be recycled because they are thermoplastics. Unfortunately, they rarely are. PUs are thermosets which are even more unlikely to be recycled. In most cases, both PUs and TPUs are landfilled or incinerated.
