What is polyurethane? Types, production and uses

Polyurethane (PU) is one of the most versatile polymer families in the chemical industry, obtained from the reaction of an isocyanate with a polyol. Starting from the same basic chemistry, mattress foam, refrigerator insulation panels, car bumpers, and industrial floor coatings can all be produced. This flexibility makes polyurethane less a single material than a material platform.

What is polyurethane?

Polyurethane is a polymer carrying a urethane bond (–NH–COO–) in its chain. This bond forms through the reaction of an isocyanate group (–NCO) with a hydroxyl group (–OH). The reaction produces no by-product and is fast; for this reason, polyurethane is often formed not in a factory but in the mold or at the point of application.

The product's character is determined by two blocks: the hard segment derived from the isocyanate and short-chain extenders (mechanical strength, hardness), and the soft segment derived from the long-chain polyol (flexibility, recovery). By varying the ratio of these two segments, both a soft foam and a rigid engineering part can be produced from the same chemistry.

How is it produced?

Production takes place by reacting an isocyanate (commonly TDI or MDI) with a polyol in the presence of a catalyst, foam stabilizer (surfactant), and blowing agent. The two components are combined in a high-pressure mixing head, and the reaction begins within seconds.

In foam production, a second reaction comes into play: the isocyanate reacts with water to release carbon dioxide, and this gas expands the mass. For this reason, the amount of water in the formulation is not merely an impurity but a direct formulation parameter. In rigid foams, additional physical blowing agents are used to improve thermal insulation; the generation-by-generation replacement of these agents due to their ozone and climate impact has defined the sector over the past thirty years.

Types and varieties

The choice of isocyanate introduces a further distinction: aromatic isocyanates (TDI, MDI) are economical but yellow under UV exposure; aliphatic isocyanates (HDI, IPDI) are used in outdoor topcoats requiring color retention and are notably more expensive.

Which sectors use it?

• Polyurethane and composites: the sector's own dedicated main category.
• Furniture and mattresses: flexible foam; the balance of comfort, density and durability.
• Construction and construction chemicals: rigid foam insulation, spray application, waterproofing, floor coating.
• Cold chain: refrigerator and cold-storage panels — among the lowest thermal conductivity values per unit thickness.
• Automotive: seating, headliners, acoustic insulation, bumpers, glass bonding.
• Paints and coatings and adhesives: the core chemistry of 2K systems.
• Footwear and leather: sole and synthetic leather coating.

Turkish market and production

Polyurethane is a growing segment of the Turkish chemical industry, driven by demand from the insulation, furniture, white goods and automotive sectors. The country is strong in system houses (formulators that turn polyols, catalysts and additives into ready-made recipes for customers) and in foam production; isocyanates and base polyols, on the other hand, are largely imported. This structure directly ties product costs to exchange rates and international raw material prices.

Topics currently on the sector's agenda include: the impact of energy efficiency regulations on rigid foam demand, blowing agent transitions (the shift toward agents with lower global warming potential), training and usage rules concerning isocyanate exposure, the use of bio-based and recycled polyols, and foam recycling (chemical recovery via glycolysis). You can follow the latest developments on these topics in the news feed below.

Technical properties

The thermal conductivity of rigid foam is among the lowest values of commonly used insulation materials; achieving the same insulation performance with a thinner cross-section is polyurethane's decisive advantage in confined spaces. However, this value rises somewhat over time (due to diffusion of the gas within the cells); for this reason, the "aged" value should be sought in data sheets.

Points to consider in selection and application

• Do not compromise on isocyanate safety. Isocyanates are respiratory sensitizers; ventilation, personal protective equipment and training are mandatory at the application site.
• Account for moisture. Water reacts with isocyanate; both the moisture content of the polyol and ambient humidity directly affect foam density and blister formation in coatings.
• Keep mold and ambient temperature stable. The reaction is exothermic and highly temperature-sensitive; seasonal changes require formulation adjustments.
• Use aliphatic topcoats outdoors. Aromatic systems yellow under UV exposure; if color retention is required, the cost difference must be budgeted for from the outset.
• Select fire behavior according to the project. In insulation applications, fire classification requirements are the primary selection criterion for the material, not a feature added afterward.

Frequently asked questions

What is the difference between polyurethane and polyurea?

Polyurethane forms from the reaction of isocyanate with polyol (hydroxyl), while polyurea forms from the reaction of isocyanate with amine. Polyurea cures much faster — within seconds — and is therefore preferred in spray waterproofing. In return, its application tolerance is narrow and requires specialized equipment.

How do you choose between TDI and MDI?

TDI is used predominantly in flexible foam, while MDI is used in rigid foam, elastomers and adhesives. MDI has lower vapor pressure, which provides a clear occupational health advantage during application and is the reason for the shift toward MDI in many applications.

Can polyurethane foam be recycled?

Since it is a thermoset, it cannot be melted and reshaped. The common route is grinding foam scrap and repressing it with adhesive (rebond — used for carpet underlay and sports flooring). In chemical recycling, polyol is recovered via glycolysis; the technology is maturing, but large-scale application remains limited.

Does higher foam density mean higher quality?

Not directly. Density is a good indicator of durability, but hardness is a separate parameter — a high-density foam can be soft, and a low-density foam can be firm. In mattresses and upholstery, the correct comparison is made by reading density and hardness (ILD) values together.

Where is spray polyurethane insulation not suitable?

On surfaces that are damp, where ambient temperature falls below the application range, and on surfaces that will be exposed to UV. Spray foam must always be protected with a coating against external factors; otherwise, its surface degrades rapidly.