GPO-3 is a high-performance, fiberglass-reinforced thermoset laminate widely used in electrical and industrial applications. Known for its excellent arc resistance, flame retardancy, and mechanical strength, GPO-3 is the material of choice for busbar insulation, switchgear housings, and other high-voltage systems. Available in sheet and rod form, it is ideal for environments that demand reliable electrical insulation and dimensional stability under stress.
In this article, we’ll explore what GPO-3 is, how it compares to FR4, and why it’s trusted by engineers, purchasers, and maintenance professionals in demanding industries.
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GPO-3 Explained
GPO-3 (or GPO3) is a glass mat-reinforced, thermoset polyester laminate that offers a unique balance of electrical, mechanical, and thermal performance. It is often referred to by the brand name Glastic®, one of the original trade names under which this material was commercialized.
Manufactured by impregnating fiberglass mats with a polyester resin and curing it under heat and pressure, GPO-3 is classified as a UL 94 V-0 flame-retardant material and complies with NEMA GPO-3 standards.
Common forms include:
GPO3 Fiberglass Sheet: Flat panels for electrical insulation and structural applications
GPO3 Rod: Used for standoffs, spacers, and turned parts
GPO3 Laminate: Custom-machined plates for structural or thermal isolation
Key Material Properties
Electrical Insulation
- Dielectric strength: Typically exceeds 300–500 volts/mil, depending on thickness
- Tracking and arc resistance: Rated excellent per ASTM D495
- UL 94 V-0 flame rating: Meets stringent fire safety requirements
Thermal Performance
- Continuous operating temperature: Up to 265°F (130°C), with short-term peaks higher
- Thermal endurance: Maintains properties even under thermal cycling
- Low thermal conductivity: Helps isolate heat in electrical assemblies
Mechanical Strength
- Flexural strength: ~20,000 psi (ASTM D790)
- Compressive strength: ~30,000 psi (ASTM D695)
- Impact resistance: Good shock and vibration performance due to mat reinforcement
Dimensional Stability
- Low water absorption: ~0.1–0.25% by weight
- Resists warping or swelling even in humid or outdoor conditions
- Stable across wide temperature and voltage gradients
Chemical Resistance
- Resistant to oils and lubricants, mild acids and alkalis, and most cleaning solvents
- Suitable for use in industrial washdown and chemical handling environments
This data is based on averages and may not relate to your specific product specs. Please contact your Piedmont Plastics sales representative for the most accurate technical data.
Applications & Use Cases
GPO-3 vs FR4: How Do They Compare?
While GPO-3 and FR4 are both fiberglass-reinforced laminates, they serve very different roles. Here’s a breakdown of how they compare:
| Property | GPO-3 | FR4 |
|---|---|---|
| Reinforcement | Fiberglass | Woven Fiberglass cloth |
| Resin System | Polyester | Epoxy |
| Dielectric Strength | Higher in thicker sections | Good across thicknesses |
| Arc Resistance | Excellent | Moderate |
| Mechanical Strength | Very high compressive & flexural | High tensile, less copressive |
| Moisture Resistance | Very low absorption | Moderate |
| Thermal Resistance | Higher Temperature resistance | Typically rated to ~130°C |
| Machinability | Easy | Brittle, prone to edge chipping |
Choosing the Right GPO-3 Material
When specifying GPO-3 for your project, consider the following:
Thickness requirements: Thicker sheets provide higher dielectric and mechanical strength.
Form factor: Choose sheet, rod, or laminate based on final part geometry.
Certifications: Look for materials rated to UL 94 V-0 and compliant with NEMA GPO-3.
Machining capacity: Discuss your needs with a supplier who can offer cut-to-size or CNC-prepped blanks.
Need help determining what GPO-3 format is right for your project? That’s where we come in.
Contact Piedmont Plastics
Piedmont Plastics is your trusted distributor for GPO-3 sheet and rod materials. With nationwide inventory, cutting and fabrication support, and technical experts on staff, we can help you source the right material for your electrical or industrial application.
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