A mold release agent (also written mould release agent) forms a very thin film between the mold and the polyurethane (PU), so the cured part separates cleanly from the mold. It is either applied to the mold or mixed into the PU system. For polyurethane foam and molded parts the main choices are water-based or solvent-based agents, semi-permanent coatings and internal release additives. The right one depends on the part, the mold, the process and whether the part is painted or bonded afterwards.
Contents
- 1. What is a mold release agent and how does it work?
- 2. Types of mold release agents for polyurethane
- 3. Wax, silicone or silicone-free: painting and bonding the part
- 4. How to choose a mold release agent by process
- 5. How to apply a mold release agent
- 6. How often to apply it and how to clean build-up
- 7. Common problems and their usual causes
- 8. Safety, VOC and the environment
- 9. JiTPOL mold release agents
- Frequently asked questions
1. What is a mold release agent and how does it work?
Polyurethane is also used as an adhesive, and liquid polyurethane that cures against a bare mold tends to bond to it. Without a barrier the part sticks and is scraped or torn when it is taken out. A mold release agent is that barrier: a thin film between the mold surface and the polyurethane, so the part separates at the film instead of tearing itself or the mold. The chemistry of the material itself is explained in our guide What Is Polyurethane?
A release agent does more than let the part out. The choice of agent and the way it is applied affect the quality and consistency of the finished part and how often the mold has to be cleaned. They also decide whether the part can be bonded or coated afterwards.
This guide covers polyurethane molding: molded flexible foam, integral skin, RIM (reaction injection molding), rigid and decorative parts, and panels from discontinuous presses. Form oils for concrete and release agents for other materials are outside its scope.
2. Types of mold release agents for polyurethane
Release agents are grouped by the carrier (solvent or water) and by how long the film lasts: used up in every cycle, semi-permanent, or built into the polyurethane.
| Type | How it works | Strong points | Watch points |
|---|---|---|---|
| Solvent-based film (external) | Wax, silicone or another active ingredient dissolved in a solvent. The solvent evaporates after spraying and the film stays. | Dries almost instantly. | Most solvents used are flammable and release VOC (volatile organic compounds), so ventilation is needed. Some solvents swell silicone rubber molds. |
| Water-based film (external) | The same kinds of active ingredients as an emulsion or dispersion in water. | Fewer health and safety concerns: the carrier is water, which is not flammable, and VOC is generally lower. | Dries more slowly. It must be completely dry before pouring, because water reacts with isocyanate and can cause bubbles and voids. |
| Semi-permanent coating (external) | Bonds to the mold surface and lasts for several cycles. | Fewer applications, because it does not have to be reapplied every cycle. | Needs a clean, dry mold surface to bond. How many cycles it lasts varies with the process, the material and the application method. |
| Internal release additive | Added to the polyurethane system itself. It migrates to the surface during cure and acts as the release film. Used in some processes, such as RIM. | Reduces how often an external agent has to be sprayed. | May not replace the external agent completely. It can keep migrating to the surface after molding and affect priming, painting and bonding. |
3. Wax, silicone or silicone-free: painting and bonding the part
Whatever the carrier, the active ingredient does the releasing: waxes, fatty esters, silicones and metallic soaps are the usual families. They differ in what they leave on the part.
- Silicone: a widely used release ingredient, but a well-known cause of paint defects. It spreads easily through the air or by touch, and very small amounts can cause craters in paint (fisheyes). Painting or gluing a part that carries silicone can therefore be difficult.
- Wax, soap and other films used up each cycle: part of the film transfers to the part, which can affect painting and adhesion. The part may need cleaning before coating; follow the paint maker's instructions.
- Silicone-free types sold as paintable: meant to leave nothing on the part that interferes with coatings and adhesives. The data sheet should say so; always confirm with your own paint and parts.
Choosing with painting in mind. Whether an agent suits your paint or adhesive is confirmed on your own parts. If you paint in the mold, the paint goes on over the release agent, so the release agent, any internal additive and the paint should be chosen together.
4. How to choose a mold release agent by process
Start from four facts: the part and its surface, the mold material, the polyurethane system (rigid or flexible), and what happens to the part afterwards. The table shows in general terms what matters most in each process.
| Process | What matters most |
|---|---|
| Integral skin parts (steering wheels, armrests) | The skin formed against the mold is the visible surface, so the release agent and the way it is applied show directly in the part and in how well it can be painted. |
| Molded flexible foam (seats, headrests, memory foam) | Production runs are often long and the foam is usually covered, so steady release and short cycles tend to count more than gloss. |
| Rigid molded and decorative parts (cornices, wood-look parts) | Fine detail and grain must come out of the mold intact. These parts are often painted afterwards. |
| Panels in discontinuous presses (cold room and sandwich panels, appliance and truck-body foaming) | The rigid foam must come away cleanly from the tooling it touches, yet stay bonded to the facings, so it matters where the release agent goes. |
The same process can call for different agents on different lines, so the final choice is best made with the supplier.
5. How to apply a mold release agent
External release agents are applied to the mold surface before the polyurethane is poured or injected, for example by spraying. Generally three things matter: a clean, dry mold at its working temperature, a thin and even film (too little agent and the part sticks, too much and agent builds up), and a film that has dried before pouring (water left in it reacts with the isocyanate and can cause bubbles and voids).
How to do this in detail depends on the type of agent, the mold and the process, so follow the technical data sheet of the agent you use. Our technical team helps you choose the right release agent and apply it on your line; see our mold release agents page.
6. How often to apply it and how to clean build-up
How often? It depends mainly on the type of agent. A film that is used up each cycle (wax, soap or similar) is renewed every cycle or every few cycles, depending on the product, the part and the mold. A semi-permanent coating lasts longer.
What build-up is. Release agent transfers to the part and to the mold. Researchers at IKV Aachen and Fraunhofer IFAM describe mold build-up as a mixture of polyurethane and release agent residue that accumulates on the mold over several cycles and makes regular, costly mold cleaning necessary, particularly for visible surfaces.
Cleaning. The right cleaner and the right cleaning interval depend on the agent, the mold material and the process, so follow the supplier's recommendations.
7. Common problems and their usual causes
Typical problems are parts that stick or tear, surface defects such as bubbles, voids or mottling, build-up on the mold, paint or glue that does not hold, and gloss or texture that varies from part to part. Their usual causes sit in a few places: the release agent and its film, the way it is applied, the condition of the mold, or elsewhere in the process, for example mold temperature, venting or mixing.
Many defects have causes unrelated to the release agent, and the same symptom can come from different causes, so the cause is best found on the line itself. Our technical team can look at the agent, its application, the mold and the system together with you.
8. Safety, VOC and the environment
Most solvents used in solvent-based agents are flammable, and these agents release more VOC than water-based agents. VOCs are organic compounds that evaporate easily, and the EU Industrial Emissions Directive defines them by their volatility. Spray areas need good ventilation, no ignition sources and equipment suited to the zone. Water-based agents have a non-flammable carrier and generally lower VOC, but the safety data sheet (SDS) of every product still applies.
Protecting people. EU Directive 98/24/EC puts substitution first, then engineering controls and collective measures such as adequate ventilation, and personal protective equipment where exposure cannot be prevented by other means. Türkiye's 2013 regulation on working with chemicals follows the same order and has the risk assessment take the supplier's Turkish SDS into account. Where flammable vapors can form an explosive atmosphere, Directive 1999/92/EC (the ATEX workplace directive) requires zone classification and an explosion protection document, and Türkiye has a 2013 regulation on this too.
Emission rules and the water-based trend. Directive 2010/75/EU (Annex VII) sets solvent emission limits for listed activities, such as coating and surface cleaning, above set solvent-use thresholds; whether a plant is covered depends on its activities and national law. Concern about solvent emissions is one reason water-based release agents for molded foam were developed; which type suits a given line depends on the process.
The polyurethane itself. Polyurethane systems contain isocyanates. In the EU, Regulation (EU) 2020/1149 requires industrial and professional users of products containing 0.1 percent by weight or more of diisocyanates to complete training before use; it has applied since 24 August 2023 and the training must be renewed at least every five years. For the health side, see What Is Polyurethane?
9. JiTPOL mold release agents
JiTPOL is a polyurethane system house in Bursa, Türkiye, and we produce our own mold release agents in water-based and solvent-based versions. They serve makers of cold room and sandwich panels on discontinuous press lines, refrigerators and hot water tanks, refrigerated truck bodies, molded seating and memory foam, integral skin and RIM parts, and decorative and wood-look parts.
Which version suits you depends on the part, the mold and how you apply the agent, so we start there and help you choose the right release agent and apply it on your line. If you paint in the mold or after demolding, tell us: our auxiliary range also includes in-mold and direct polyurethane paints. Release agents can be quoted on their own or together with a JiTPOL two-component system, and for suitable projects our technical team can visit your line and run production trials with you. Details and the quote request are on our mold release agents page; we send the technical data sheet of the agent proposed for your line on request.
Frequently asked questions
Should I use a water-based or a solvent-based mold release agent?
It depends on the part, the mold, the process and your plant's rules. Solvent-based films dry almost instantly, but most solvents used are flammable and release VOCs. Water-based films raise fewer health and safety concerns, but they dry more slowly and must be fully dry before pouring, because water reacts with isocyanate.
What is a semi-permanent mold release agent?
A coating that bonds to the mold surface and keeps releasing for several cycles, so it does not have to be applied every time. How many cycles it lasts varies with the process, the material and the application method. It needs a clean, dry mold surface, and the supplier's data sheet describes how it is applied and renewed.
What is an internal mold release agent?
An additive mixed into the polyurethane system. It migrates to the surface during cure and acts as the release film. It is used in some processes, such as RIM. It reduces how often an external agent has to be sprayed but may not replace it, and because it can keep migrating to the surface it may affect priming, painting and bonding. Test it with your own system.
Can I paint a part made with a release agent?
Often yes, but the release agent decides how easy it is. Release agent residue often has to be cleaned off before painting or bonding, and silicone is a known cause of craters in paint, even in very small amounts. Silicone-free types sold as paintable are meant to avoid this problem. Confirm the combination of agent and paint on your own parts.
How often should I apply mold release agent?
It depends mainly on the type of agent. A film that is used up each cycle is renewed every cycle or every few cycles, while a semi-permanent coating lasts longer; how long depends on the product, the part and the mold. More agent is not better, because excess builds up on the mold. The right interval is best set with the supplier.
Why does my polyurethane part stick to the mold?
Usually the release film is not doing its job: it may be too thin, uneven or used up, the agent may not suit the polyurethane system, or the condition of the mold or the process may be making it harder for the film to work. The cause differs from line to line, so check the agent's technical data sheet first and talk to our technical team if the problem stays.
Is solvent-based mold release agent flammable?
Usually yes: most solvents used in release agents are flammable, so solvent-based agents give off flammable vapors. Spray in well-ventilated areas without ignition sources, use equipment suited to the zone, and wear the protective equipment named in the safety data sheet (SDS). Water-based agents have a non-flammable carrier, but their SDS applies too.
Sources
- Wikipedia: Release agent
- Wikipedia: Polyurethane
- Hopmann et al., PU Magazine 6/2020 (IKV Aachen, Fraunhofer IFAM)
- Schöldgen et al., European Polyurethane Journal, September 2014 (IKV Aachen, Fraunhofer IFAM)
- Hutchinson (1987): internal mold release in PU-RIM, primer wetting and heat migration
- Thompson and Suddaby, SAE 1991: internal mold release in RIM polyurethane
- US patent 5,028,366 (Air Products, 1991): water-based release agent for molded foam
- Abdul-Rani et al. (2005): mold temperature and foam surface texture
- Lee, Park and Whitesides (2003): solvents swell silicone rubber (PDMS)
- National Collision Repairer (2021): silicone contamination in the paint shop
- HMG Paints: cratering and fish eyes
- Directive 2010/75/EU: VOC definition, Annex VII
- Directive 98/24/EC, Article 6: chemical agents at work
- EU-OSHA: Directive 1999/92/EC, explosive atmospheres
- Resmî Gazete 28733 (2013): regulation on working with chemicals
- Resmî Gazete 28633 (2013): regulation on protecting employees from explosive atmospheres
- Commission Regulation (EU) 2020/1149 (diisocyanates, REACH Annex XVII)