Polyurethane Resin

Synonym: Urethane resin PU resin

Urethane (Polyurethane) resins are copolymers consisting of polyol and isocyanate components, Before curing, Resin is an organic compound that comes in a liquid form. When Parts A and B are mixed in proper proportion (1A:1B by weight),  cures at room temperature with virtually no shrinkage. Once dried, it forms into a strong and durable plastic.

Principle of Curing

Generally speaking, Polyurethanes are formed by reacting a polyol (an alcohol with more than two reactive hydroxyl groups per molecule) with a diisocyanate or a polymeric isocyanate in the presence of suitable catalysts and additives.


  1. Low Viscosity, excellent flow properties
  2. Good filling capacity
  3. Hardens quickly and its demolding time is very short
  4. Only a small amount of shrinkage during curing
  5. High heat resistance after curing
  6. Higher bubble formation, venting is difficult
  7. Very high strength
  8. High abrasion resistance
  9. Good acid resistance


Polyurethane resin is a fascinating material for both industry and the do-it-yourselfer. Due to its low viscosity and various other properties, polyurethane resin is ideally suited for mold casting, especially as a reproduction of water bodies.

Polyurethane resin has high compressive and flexural strength, durable and cure with low shrinkage. Ideal for making industrial parts, foundry patterns, vacuum forming molds, and some ceramic applications.

Applications include reproducing small to medium size sculptures, making prototype models, resin Jewelry,special effect props, decorative jewelry,  and taxidermy (bones, antlers, teeth etc.). Colors and/or fillers can be added for an infinite variety of casting effects.

Because Polyurethane resin is a fast curing resin and becomes hard quickly, it is also great for doing fast cold cast bronze, brass, copper, nickel/silver and other metals.

How to Use

Step 1: Applying A Release Agent

A release agent is necessary to facilitate demolding when casting into or over most surfaces. silicone rubber molds usually do not require a release agent unless casting silicone into the mold. Applying a release agent will prolong the life of the mold.

Step 2: Measuring & Mixing

Liquid urethanes are moisture sensitive and will absorb atmospheric moisture. Mixing tools and containers should be clean and made of metal, glass or plastic.

After dispensing equal amounts of Parts A and B into mixing container (100A:100B by weight) and mix thoroughly.

Step 3: Pouring

For best results, pour your mixture in a single spot at the lowest point of the containment field and let the mixture seek its level. This will help minimize air entrapment.

Step 5: Vacuum pumping (optional)

If Vacuum Degassing subject mixture to 29 inches mercury for 3 minutes or until mixture rises and falls.

For Best Results . . . Best results are obtained using a pressure casting technique. After pouring the mixed compound, the entire casting assembly (mold, dam structure, etc.) is placed in a pressure chamber and subjected to 60 PSI air pressure for the full cure time of the material.

Step 5: Curing

Demold time of the finished casting depends on mass and mold configuration. Low mass or thin-walled castings will take longer to cure than castings with higher mass concentration.


  1. Because no two applications are quite the same, a small test application to determine suitability is recommended if performance of this material is in question.
  2. All liquid urethanes resin are moisture sensitive and will absorb atmospheric moisture, which can cause undesirable reactions such as foaming.
  3. During the curing process, also pay attention to the heat given off by the exothermic process. In large castings, it can sometimes cause thermal shrinkage or distortion.
  4. You must, pay attention to the pot life, otherwise the material hardens too quickly, and you have to start again from the beginning.
  5. The mixing time, pot life and pouring time depend on the temperature, the environment and the relative humidity value and with resins depending on the volume.


  1. When storing polyurethane resin, care must be taken to avoid large temperature fluctuations. In general, PU resin should be stored at a temperature of 15 to 25 degrees Celsius in closed containers.
  2. Make sure that the packaging is airtight and moisture-proof when opened. Shelf life of product is reduced after opening. Remaining product should be used as soon as possible. Immediately replacing the lids on both containers after dispensing product will help prolong the shelf life of the unused product.


  1. During curing, the styrene causes a strong odor and thus a potential health hazard. Be sure to wear a proper respirator, and proper protective gloves, eye protection, skin protection, and clothing protection. Also, make sure your work area is well ventilated.
  2. The isocyanates contained in polyurethane resin are allergenic. However, these properties only apply to the material that has not yet reacted. Once the reaction is complete, no further health hazards are to be expected from the material.
  3. Avoid open fire in the vicinity. Should the mixture come into contact with your eyes or mucous membranes, rinse them thoroughly for several minutes and then consult a doctor.
  4. Castings will be extremely hot immediately following cure and may burn the skin. Let cool to room temperature before handling.
  5. Adult Supervision Required. Keep Out of the Reach of Children.