Opti-tec 4220 Semi-opaque, Translucent Polyurethane Encapsulant for Electronics and LED Potting


Opti-tec™ 4220 is a two-part, flexible, room temperature curing polyurethane resin, designed for potting, encapsulation and protection of LED arrays and other lighting products. Opti-tec 4220 cures to form a semi-opaque, milky, translucent material (opalescent) which still allows a high transmission of light. It provides aesthetically pleasing encapsulation, hiding underlying electronics and providing a diffuse light. The material is suitable for outdoor use, with excellent weathering properties; it is formulated with UV resistant materials and includes UV stabilisers.

The opalescent properties of Opti-tec 4220 compared to Opti-tec 4200 in cured samples
The opalescent properties of Opti-tec 4220 compared to Opti-tec 4200 in cured samples
Opti-tec 4220 can be used to encapsulate LED uplights
Opti-tec 4220 can be used to encapsulate LED uplights

Features & Benefits

  • Cures to form milky, opalescent plastic
  • Conceals electronics whilst giving high light transmission
  • Can be used outdoors – excellent long term UV stability and weather resistance
  • Scratch and mark resistant
  • Low viscosity – easy to mix and process
  • High mechanical strength
  • Non-toxic


  1. Potting of LED lighting projects, including LED tracks, arrays, luminaires
  2. Protection of electronics located outside or walked on; uplighters
  3. Decorative lighting
  4. Optical instruments


Resin Hardener Mixed
Colour Clear Clear Translucent milky-white (when cured)
Specific gravity (g/ml) 1.04 1.16 1.10
Viscosity mPa.s @ 25°C 600 600 600
Mix ratio by weight 0.90:1
Mix ratio by volume 1.00:1
Curing (typical values – will vary according to mass and application. Higher cure temperatures will result in greater cure shrinkage and exotherm)
Pot life (150g mix @ 20-25°C) 20 minutes
Gel time (150g mix @ 20-25°C) 30 minutes
Light handling 24 hours @ 20-25°C
12 hours @ 40°C
6 hours @ 60°C
Full cure 48 hours @ 20-25°C
24 hours @ 40°C
12 hours @ 60°C
Cured properties
Water absorption 0.87% (30 days @ 25°C)
Shore D hardness 30
Operating temperature (application & geometry dependant) -55 to +120°C
Thermal conductivity 0.25 W/mK
Tensile strength 46 mPa
Elongation at break 2-4%
Compressive yield strength 60 mPa
Coefficient of linear expansion 60-80 pp/m°C
Volume resistivity 1.3 x 1013 ohm.cm
Surface resistivity 1.4 x 1012 ohm
Electric strength 20 kV/mm
Opti-tec 4220 is RoHS compliant and contains 0% REACH SVHC

Ordering Information

Opti-tec 4220 is available in bulk, twinpacks and cartridges.

Part number Description
OPT4220-50G Semi-Opaque Polyurethane Encapsulant – 50 gram double syringe cartridge
IDM805001 Syringe Gun – for 50g cartridges
OPT4220-250G Semi-Opaque Polyurethane Encapsulant – 250 gram twinpack sachet
OPT4220-2KG Semi-Opaque Polyurethane Encapsulant – 2 kg bulk kit

For the best results, store in conditions that aren’t humid and store away from strong bases, strong acids, strong oxidising agents, strong reducing agents, water, amines and alcohols. Keep in the original packaging and store in a cool, well-ventilated area. Keep container tightly closed.

  • Last updated: July 2019
  • Version: 2.2

Statements, technical information and recommendations contained herein are based on tests we believe to be reliable but they are not to be construed in any manner as warrantees expressed or implied. The user shall determine the suitability of the product for his intended use and the user assumes all risk and liability whatsoever in connection therewith.