VFI®-4281 78 D Polyurethane Casting Plastic

VFI-4281 78 D Polyurethane Casting Plastic is a high-impact urethane plastic with high heat deflection and tensile strength. This material works well when vacuum-degassed and pressure-potted to provide a repeatable, uniform, void-free cast. It is a multi-faceted plastic capable of being used in rapid prototyping, production parts, and equipment housings for large part runs. VFI-4281 has a working time of 6-8 minutes.  

VFI-4281 78 D Polyurethane Casting Plastic is a high-impact urethane plastic with high heat deflection and tensile strength.

Features & Benefits

  • Usable in platinum-cured silicone, metal, or prototyping urethane molds
  • High heat deflection temperature (HDT) at 199.04°F (92.8°C)
  • Neutral color for easy priming and top coat application
  • Excellent processing and demold times at 1-2 hours
  • Non-mercury based, TDI-free, MOCA-free, odorless polymer

Instructions for Use:  

Mold Preparation  

VFI recommends using a release agent for molding applications to extend the life of the mold. For prototyping urethane molds, using a release agent is required. Heated molds or any mold over 120°F are not recommended because it will cause an uneven cure. 

Casting Process  

The B side (Poly) of VFI-4281 78 D Polyurethane Casting Plastic must be premixed once daily before each use. Be careful not to introduce extra moisture or air into the mix. Prepare a container that is an appropriate size with at least 2/3 of head space for vacuum degassing. Pour the measured A side into the container, and then pour the measured B side into the same container. Mix the material until uniform with a hand or power mixer. You must finish mixing, vacuum degassing, and pouring before the end of the pot life. 

For a fully cured part, VFI-4281 cannot be poured less than a quarter inch thick at room temperature. If thinner pours are needed, you must elevate the mold and molding temperature to 115°F.  

After curing at room temperature for 16 hours, a heat cure at 150°F for 24 hours is recommended to achieve full physical properties. If you do not post-cure the material in an oven, physical properties will be delayed until after seven days or may not fully develop.  


*Always read the safety data sheet before working with chemicals  

Use chemicals only as directed and for their intended purpose. Do not dispose of chemicals down the drain. Most chemicals must be disposed of as hazardous waste. 

PPE to avoid all unnecessary exposure:  

  • Eye protection – wear approved safety glasses and any additional eye protection as necessary 
  • Hand protection – wear chemically resistant protective gloves (nitrile, butyl, or neoprene) 
  • Skin and body protection – wear suitable protective clothing 
  • Respiratory protection – in case of insufficient ventilation, wear suitable respiratory equipment. Respirator selection must be based on known or anticipated exposure levels, the hazards of the product, and the safe working limits of the selected respirator 

Product Limitations  

This product contains isocyanate, which may irritate the skin and is toxic if inhaled.  

  • Incompatible materials – A side: amines, strong bases, water, alcohols, and heavy metals. B side: oxidizers  
  • Conditions to avoid – A side: contamination with water; keep away from heat, ignition sources, and incompatible materials. B side: heat and incompatible materials 
  • Chemical stability – stable under normal storage conditions 
  • Reactivity & hazardous reactions – no dangerous reaction known under normal use  
  • Hazardous decomposition products – may include, but are not limited to, oxides of carbon. Also, oxides of nitrogen and isocyanates for the A side 

Potential Health Hazards 

  • May cause respiratory irritation. A side material may also cause allergy and asthma symptoms or breathing difficulties.  
  • May cause stomach distress, nausea, or vomiting if swallowed.  
  • May cause skin irritation and sensitization: redness, edema, drying, defatting, and cracking.  
  • May cause eye irritation: discomfort, pain, excess blinking and tear production, marked redness, and swelling of the conjunctiva.  

*If you are experiencing any of these symptoms, seek medical advice or attention. Call a poison control center or doctor if swallowed.   

Application Methods:

  • Pour

Available Packaging:

  • Drum
  • 5 Gallon

Physical Properties

  • Hardness Shore D: 78
  • Tensile Strength: 8850 psi
  • Tensile Modulus: 250,000 psi
  • Elongation: 10%
  • Flexural Strength: 12,300 psi
  • Flexural Modulus: 281,000 psi
  • Shrinkage Linear: <0.01 in/in
  • Izod Impact, Notched: 0.72 ft-lb/in
  • Izod Impact, Unnotched: 9.20 ft-lb/in
  • Heat Deflection Temperature (HDT): 199.04 °F ± 2 °F

Liquid Properties

  • Mixed Solids by Volume: 100%
  • Liquid Density A Side: 9.5 lbs/gal
  • Liquid Density B Side: 8.9 lbs/gal
  • Mixed Liquid Density: 9.3 lbs/gal
  • Specific Gravity A Side: 1.14 g/ml
  • Specific Gravity B Side: 1.07 g/ml
  • Mixed Specific Gravity: 1.11 g/ml
  • Ratio by Volume (A:B): 100A:53.3B
  • Ratio by Weight (A:B): 2A:1B
  • Viscosity A Side: 100 cps
  • Viscosity B Side: 2300 cps
  • Mixed Viscosity: 300 cps
  • Pot Life: 8 minutes
  • Gel Time: 10 minutes
  • Flash Point: >200 °F

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