Flex Circuit Material Properties

Below you will find a chart depicting the typical properties of dielectric material used in flexible printed circuit boards. You can also see our blog post on adhesive and adhesiveless polyimide flex core material types for additional information.

Typical Properties of Dielectric Material for Flexible Printed Circuitry

Property (Typical) Units Polymide Polymide (Adhesiveless) Polyester
Representative Trade Name   KAPTON KAPTON MYLAR
Thickness Range mil 0.5 to 5 1-6 2-5
Tensile Strength (@25°C) psi 25,000 50,000 20,000 to 35,000
Break Elongation % 70 50 60 to 165
Tensile Modulus (@25°C) 100,000 psi 4.3 .7 5
Tear Initiation Strength lb/in 1000 700-1200 1000 to 1500
Tear Propagation Strength g/mil 8 20 12 to 25
Resistance to:        
Strong Acids   Good Good Good
Strong Alkalis   Poor Good Poor
Grease and Oil   Good Good Good
Organic Solvents   Good Good Good
Water   Good Good Good
Sunlight   Good Good Fair
Fungus   Non-nutrient Non-nutrient Non-nutrient
Water Absorption % (24 hours) 2.9 0.8 <0.8
Service Temperature (min/max) degree C -125/+200 -125/+200 -60/+105
Coefficient of Thermal Expansion (@22°C) PPM/degree C 20 20 27
Change in Linear Dimensions (100°C, 30min) % <0.3 0.04-0.02 <0.5
Dielectric Constant (ASTM D150) 1MHz   3.4 3.4 3
Dissipation Factor (ASTM D150) 1MHz   0.01 0.003 0.018
Dielectric Strength (ASTM D149)
@ 1 mil thickness
Volume Resistivity (ASTM D257)
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