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Ecoflex™ 5

Ecoflex™ 5 vs. Smooth-Cast® 305 vs. Smooth-Cast® ONYX™ FAST

Super-Soft, Addition Cure Silicone Rubber

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Smooth-Cast® 305

Ecoflex™ 5 vs. Smooth-Cast® 305 vs. Smooth-Cast® ONYX™ FASTEcoflex™ 5 versus Smooth-Cast® ONYX™ FAST

Bright White, Ultra Low Viscosity Liquid Plastics

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Key Differences

Product Type
  • Silicone Rubber - Platinum Cure
  • Urethane Resins
  • Urethane Resins
Mixed Viscosity13,000 cps100 cps80 cps
Pot Life1 minute2.5 minutes7 minutes
Cure Time5 minutes15 minutes30 minutes
Shore D Hardness8070
Shore A Hardness5
ColorTranslucentBlackWhite
Tensile Strength350 psi5,840 psi3,000 psi
Elongation @ Break1,000 %4 %7.5 %
Disclaimer
Although we do our best to ensure the accuracy of this Compare Tool, Smooth-On offers no warranty either expressed or implied as to the reliability of the information contained herein. Smooth-On assumes no liability for loss or damage associated with use of the Compare Tool. If this is a critical project, we encourage you to review all of the technical data below and contact our Technical Service department with any questions or concerns.

All Technical Data

Ecoflex™ 5Smooth-Cast® ONYX™ FASTSmooth-Cast® 305
Product Type
  • Silicone Rubber - Platinum Cure
  • Urethane Resins
  • Urethane Resins
Mixed Viscosity13,000 cps100 cps80 cps
Mix Ratio By Volume1A:1B100A:100B1A:1B
Mix Ratio By Weight1A:1B120A:100B100A:90B
Pot Life1 minute2.5 minutes7 minutes
Cure Time5 minutes15 minutes30 minutes
Shore D Hardness8070
Shore A Hardness5
Specific Gravity1.07 g/cc1.09 g/cc1.05 g/cc
Specific Volume25.8 cu. in./lb.27.7 cu. in./lb.26.4 cu. in./lb.
ColorTranslucentBlackWhite
Die B Tear Strength75 pli
Tensile Strength350 psi5,840 psi3,000 psi
Tensile Modulus246,000 psi134,000 psi
Elongation @ Break1,000 %4 %7.5 %
100% Modulus15 psi
Compressive Strength8,760 psi3,800 psi
Compressive Modulus77,400 psi44,900 psi
Flexural Strength8,280 psi4,000 psi
Flexural Modulus246,000 psi118,000 psi
Shrinkage<.001 in. / in.0.010 in. / in.0.0065 in. / in.
Heat Deflection Temp120 °F
Useful Temperature (min)-65 °F
Useful Temperature (max)450 °F
Heat Deflection With Post Cure250 °F

Product Description

Ecoflex™ 5

Ecoflex™ rubbers are platinum-catalyzed silicones that are versatile and easy to use. Ecoflex™ rubbers are mixed 1A:1B by weight or volume and cured at room temperature with negligible shrinkage.  Low viscosity ensures easy mixing and de-airing. Dispense using our convenient dispensing cartridges. Cured rubber is very soft, very strong and very “stretchy”, stretching many times its original size without tearing and will rebound to its original form without distortion.

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Smooth-Cast® ONYX™ FAST

Smooth-Cast® ONYX™ is a mercury-free urethane resin that cures at room temperature to a deep black, solid plastic. ONYX™ resins offer the convenience of a 1A:1B by volume mix ratio and have very low viscosities, so they are easy to mix and pour. ONYX™ resins have an ultimate Shore hardness of 80D and offer higher physical properties and higher heat resistance vs. other general purpose resins.ONYX™ FAST resin has a pot life of 2.5 minutes and a cure time of 10-15 minutes. ONYX™ FAST is a good choice for creating fast cold cast bronze, brass, copper, nickel/silver, etc. effects.

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Smooth-Cast® 305

The Smooth-Cast® 300 Series of liquid plastics are ultra-low viscosity casting resins that yield castings that are bright white and virtually bubble free. Vacuum degassing is not necessary. They offer the convenience of a 1A:1B by volume or 100A:90B by weight mix ratio. The differences between them are pot life and demold time.

These resins readily accept fillers (such as URE-FIL® 3 from Smooth-On) and can be colored with SO-Strong® or Ignite® color tints (Smooth-Cast® 325 series accepts pigments better than the Smooth Cast® 300 series). Fully cured castings are tough, durable, machinable and paintable. They resist moisture and mild solvents. Applications for Smooth-Cast® 300 Series Liquid Plastics include reproducing small to medium size sculptures, making prototype models, special effect props and decorative jewelry.

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