Polyurethane Resin

Polyurethane Resin – A Look at Polyurethane Casting Resin

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When working with resin, there are a plethora of options available. You can choose various resin types, each of which has specific benefits that make it suited for a particular purpose. There are, of course, also downsides to keep in mind – especially when dealing with polyurethane resin. In the guide that follows, we will look at the different characteristics of these products and give you a clue as to what to keep in mind when making your choice of polyurethane resin for your project.



What Is Polyurethane Resin?

Technically, polyurethane (PU) is a synthetic resin or plastic produced by a reaction between polyisocyanates, polyols, and dialcohols. The numerous characteristics of polyurethane resin differ depending on the application purpose, allowing for many options. You can create thermoplastics along with thermosets and elastomers from polyurethane resin.

Usually, polyurethane casting resins consist of a dual-component protocol, consisting of hardener and resin. The chemicals then react when these are combined, causing the mixture to solidify. Like epoxy and polyester resin compounds, PU resin can be mixed with different additional ingredients and colorants or filling materials. This allows certain for characteristics, such as increasing the activity window by using an inhibitor to slow the curing process. The resulting mixture can be optimized for various purposes.

You can also add fluorescent dyes and color pigments to PU resin in order to produce various colors. This enables you to customize the resin for your specific needs. There are fillers for instance, such as glass fibers, lightweight fillers, cotton flocks, and mineral fillers. Adding them can affect the elasticity, durability under stress, or the rigidity of the surface.

Polyurethane Casting


Advantages and Disadvantages of Polyurethane Resin

Before purchasing polyurethane resin, you will need to find out which of the usage characteristics are well suited to your needs. Usually, polyurethane casting resins offer an easy-to-use solution with plenty of beneficial aspects and only a few problem areas.


  • Great fluidity, allowing easy mixing and application
  • Viscosity is low enough to provide optimal casting and shaping
  • Hardens rapidly with a minimal demolding time
  • Comes in handy when producing miniature models and for insulation of electrical wiring
  • Remains extremely durable
  • Allows for the combining of a range of different additives like filling agents, inhibitors, and color pastes
  • Extreme heat resistance once properly cured
  • Some PU resins allow for the use of elastomers and thermosetting plastics – once the curing is complete, elastomers can be joined together through vulcanization


  • Moisture sensitivity can make it prone to foaming
  • Additives are required for adequate UV resistance
  • Welding not possible once curing is complete
  • Styrene emits toxic fumes while curing, which is potentially dangerous
  • Adhesion not as strong as that of epoxy resin

Polyurethane casting resins that require a brief application procedure and allow for fast unmolding are usually referred to as fast-casting resins. The active pot life once the resin is mixed should be closely monitored when working with it. If it hardens too suddenly you may spoil the entire application and have to start again. Whille this may seem an inconvenience, it does makes it faster to unmold.

When purchasing polyurethane resin, be sure to find out how hard the mixture sets when cured and what will actually suit your needs. Shore indicates the hardness level. You can easily find out the shore of a material by checking the description on the packaging.

Once cured, softer, more rubber-like materials are shown in Shore hardnesses 00 to A, while harder materials are in Shore hardnesses A to D. The number value will indicate where exactly your material falls on the shore hardness scale (where higher numbers indicate increased hardness). For example, most PU resins have a Shore hardness of 80 to 95A. 



Application Areas of PU Resin

Polyurethane resin is extremely versatile in its various application purposes. Polyurethane casting resins are ideal for both the home DIY enthusiast and in industrial situations. Foams can be created from polyurethane, for instance, and in coatings, adhesives, and paints too.

Polyurethane also provides protection from moisture or mechanical stress in the manufacturing of electronics – these assemblies are generally encapsulated. Polyurethane resin is also essential in the manufacturing of damping elements, drive elements, and instrument transformers.

In foam manufacturing, the foam formation produced needs to react with water, whereas in other applications, the surface needs to be dry when the liquid polyurethane comes into contact. The beneficial properties of the casting resin may become weakened if not applied correctly.

Polyurethane Casting Resin


Floor Coatings

Polyurethane resins are widely used for industrial flooring like in-car workshops, warehouses, or halls. Not only does it look impressive, but it offers excellent protection for the floor underneath. These floors are usually concrete, so reinforcement for large loads and wear and tear is essential, and the resin coating also offers other benefits too. It provides a layer of scratch and abrasion resistance, as well as the elasticity to deal with temperature changes and moving loads.

The application process is simple, and it is a rather cost-effective solution.

When used outdoors, PU resin has advantages over epoxy resin in that its UV resistance prevents yellowing and it can withstand sudden changes in temperature. Polyurethane coatings are also commonly used in schools and kindergartens because of their safety benefits, as they reduce the risk of slipping considerably.

Polyurethane casting resin is also commonly used when renovating flat rooftops. It offers some great benefits, including its lasting durability and ease of application. The UV-resistant properties of the material are also extremely useful here.


Best Polyurethane Resin for Flooring: LIQUID RUBBER Smooth Polyurethane Deck Coating

This glaze coat kit is a single-component, low-VOC urethane coating that can withstand extreme conditions. This coating offers protection while upgrading the surface with its impressive appearance. It provides a durable, industrial-grade coating whilst still allowing the underlying floor to breathe. This flooring coat is ideal for garages, wooden decks and even metal surfaces, as it offers good resistance against scratches and chemicals and UV damage.

LIQUID RUBBER Smooth Polyurethane Deck Coating
  • High-performance polyurethane coating covers 40 sq. ft. per gallon
  • Dries hard to a durable waterproof surface with excellent UV stability
  • Suitable for concrete, wood, non-corroded metal, pool decks, and more
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  • Ease of application
  • Effective area coverage
  • Weather-resistant
  • Low-VOC formula
  • Good resistance to chemicals
  • Protects against scratches


  • Non-professionals my struggle to achieve a smooth finish


Polyurethane Casting Resin for Mold Casting

In the process of casting a mold, the two polyurethane components are combined and then poured into the mold, and after some time this mixture will harden. Liquid polyurethane is very well-suited for mold casting due to its low viscosity and a variety of other benefits. Mold castings can be used in some of the following situations:

  • The manufacturing and encapsulation of electronic components, like insulation, assemblies, and semiconductors;
  • Restoration and renovation of buildings and monuments;
  • Packaging fragile objects and also for use as transparent sealing;
  • Glazing and coating of a variety of items;
  • Model making, especially to reproduce bodies of water; and
  • Sealing the contacts of cables.

When casting polyurethane resin, you will need to consider that a polyurethane casting can only be removed from the mold if the mold was pretreated with a releasing agent. It is also worth keeping in mind that you may not be able to keep or reuse the mold afterwards, as the reaction from elastic polyurethane releases high heat levels as it cures, which can damage the master model.

Mold casting is widely used in both commercial and domestic situations, and allows for application with machinery or manually. Thorough mixing and careful pouring of the resin is essential, or the process may produce air bubbles. Once you have finished pouring the resin, give the mold a few gentle taps to ensure that the mixture settles and avoids air bubbles.

polyurethane casting resin

It is also possible to fill the mold from above, which is a safer method for preventing air from combining with the mixture. In industrial situations, the compound and the cast are pre-dried and degassed with a vacuum to help this process. 


Best Polyurethane Casting Resin: SPRESIN Model-Pro Polyurethane Casting Resin

This dual-component polyurethane resin contains no solvents and emits only a low odor. It is also impact-resistant and has the durability needed for various applications. This polyurethane casting resin is well-suited for building prototypes, models, molds, and figurines, and offers a range of uses for both DIY enthusiasts and skilled craftsmen.

SPRESIN Model-Pro Polyurethane Casting Resin
  • A two-component polyurethane casting resin used in model-making
  • High strength and impact resistance, along with low viscosity 
  • One-gallon kit of resin and hardener is versatile and free of solvents
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  • Odorless and free of solvents
  • Easy to use
  • 15-minute curing time
  • Can be machined or painted


  • Working time of only 2.5 minutes
  • Not as simple as single-component products



Step-by-Step Instructions for Processing Polyurethane Casting Resin

The application process used with cast polyurethane is dependent on what purpose you are using it for. In the following instructional guide, we will look at mold casts as well as using polyurethane resin for coating flooring.

  • The time period during which you can effectively apply a dual-component resin is short, so be sure you have all your ingredients, materials, and tools ready before you begin working with the cast polyurethane. If necessary, reduce the amount of combined mixture or use an inhibiting agent when working with large surface areas or molds.
  • Give the floor a thorough cleaning before you begin the mixing process. Ensure there is no trace of dirt, grease, or dust, and then you can go about filling any gaps, cracks, or inconsistencies so that the surface is completely smooth. Before applying any cast polyurethane, make sure the sealant has dried.
  • You can then begin priming the floor with a polyurethane-based, solvent-free primer.
  • If it is a dual-component product, you can now start mixing the polyurethane resin mixture. If you are working with a single-component resin, simply proceed to the next step.
  • Ensure that you follow the product guide carefully when you combine the ingredients. Pour the resin between the two containers and stir it well so it is properly blended.
  • Once the mixing is complete, you can begin applying the polyurethane resin or pouring it into the mold. The floor coating layer is generally a few millimeters thick, but for other applications, this will depend on what type of project it is. If you need to cast a mold, it must be properly pretreated with a release agent.

  • The resin then needs to cure in its own time once the application is complete. There are both cold- and hot-curing resins, and the type you are working with will determine the length of the curing process. Some urethane resin types can even make use of a UV lamp for curing.
  • Approach the casting of larger objects with caution, as shrinking is common during the curing of wider areas. Re-casting will fix this, but avoid any air holes or inconsistencies on the surface. Once the curing is complete, further re-casting is not recommended, as the risk of cracking or placing stress on the material internally is high.
  • Monitor the heat from the exothermic reaction during the curing process carefully. If necessary you may need to help the heat to dissipate, as too rapid a rise in the temperature could cause the resin to harden too rapidly and unevenly, resulting in inconsistent quality and durability.
  • Polyurethane resin cast items allow further processing once they have been cleaned and the releasing agent has been fully removed. It is then possible to add a primer coat or paint them. Should the item be for outdoor use, you might need to paint it for the protection provided against UV rays and weather degradation.

Applying Polyurethane Resin


Storage and Durability of Polyurethane Casting Resins

It is essential to regulate temperature as much as possible when storing polyurethane resin. It is usually optimal to keep PU resin sealed at 59 to 77 degrees Fahrenheit (15 to 25℃). Ensure the packaging is moisture-proof and airtight once opened. When in use, give each component a careful shake before combining the ingredients, and try to limit the time that each container is open as much as you can.

While storing them, polyurethane casting resins may be prone to crystallization. To restore the fluidity for use again, very gradually heat the resin to a maximum temperature of 158 degrees Fahrenheit (70℃). Ensure that it has cooled to room temperature before attempting to work with it.


Safety Precautions for Applying Polyurethane Casting Resin

  • Polyurethane casting resins contain isocyanates, which are allergenic as well as carcinogenic, but these toxic chemical properties exist only in the substance before reacting when mixed. Ensure you have all the necessary precautions in place when working with PU resin.
  • Certain additives can be hazardous, like flame retardants and plasticizers.
  • Remember to read all safety documentation supplied with PU resin. Wear protective equipment such as safety gloves, goggles, long sleeves, and a respirator mask at all times when working with the substance. Select a workspace with good airflow and ensure all the necessary tools required are nearby for quick access.
  • Never allow polyurethane near an open flame. If you manage to get the mixture in your eyes or nose, immediately begin rinsing them and seek medical attention without delay.


Clear Polyurethane Resin



Frequently Asked Questions


What Is Polyurethane?

Polyurethane resin finds use in so many day-to-day situations. Its usage characteristics are beneficial for commercial as well as home use. The production process involves an exothermic polyaddition reaction, which releases heat. Polyurethane, for this reason, is diverse in the range of different application purposes it offers, both at home and in commercial sectors. The numerous beneficial qualities and simple application process will allow you to achieve the results you want while requiring little or no experience.


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