A Guide to ASTM D257 for Surface & Volume Resistivity
ASTM D257, IEC 62631-3-1 test method determines surface resistivity and volume resistivity of insulating materials. Indirect measurements of moisture content, degree of cure, mechanical continuity, or different types of deterioration are frequently made using the values of resistivity or conductivity. The degree of correlation found by supporting theoretical or experimental investigations determines how helpful these indirect measurements are. The low-frequency dielectric breakdown and dissipation factor characteristics of materials can be predicted by resistivity values. Read more about ASTM D257 below.
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- Overview
- Scope, Applications, and Benefits
- Test Process
- Specifications
- Instrumentation
- Results and Deliverables
Overview
ASTM D257 describes the standardized test method for determining DC electrical resistance or conductance of insulating materials. It deals with surface and volume resistivity, essential factors in measuring a material’s ability to resist the flow of electric current.
The test is widely used in electrical engineering and materials science to verify insulation performance, ensure electrical safety, and support material selection and quality control for electrical and electronic components.
Scope, Applications, and Benefits
Scope
ASTM D257 outlines procedures for measuring the electrical resistivity of insulating materials under controlled environmental conditions.
It evaluates:
- Surface resistivity (resistance to leakage current across the surface)
- Volume resistivity (resistance to current flow through the bulk material)
- DC resistance or conductance of insulating materials
The test requires controlled temperature and humidity, specific electrode configurations, and calibrated resistance-measuring equipment to ensure accurate results.
Applications
- Selection of insulating materials for electrical and electronic components
- Evaluation of plastics and polymers used in electrical insulation
- Quality control and compliance testing for electrical products
- Performance assessment of materials in semiconductors, aerospace, medical devices, and renewable energy systems
- Insulation testing to prevent electrical leakage and system failures
Benefits
- Determines the insulation effectiveness of materials
- Supports safe and reliable electrical system design
- Enables comparison of resistivity among different materials
- Assists in quality control and specification compliance
- Provides standardized, repeatable, and reliable test results
Test Process
Specimen Preparation
Test specimens are prepared according to the required dimensions and conditioned under controlled temperature and humidity.
1Test Setup
Electrodes are applied to the specimen using standardized configurations, and the sample is placed in a controlled test environment.
2Resistance Measurement
A DC voltage is applied using a megohmmeter or insulation resistance tester to measure surface and volume resistance.
3Data Evaluation
Surface and volume resistivity values are calculated and recorded for material comparison and analysis.
4Technical Specifications
| Parameter | Details |
|---|---|
| Test Principle | Measurement of DC resistance or conductance of insulating materials |
| Measured Properties | Surface resistivity, volume resistivity |
| Sample Types | Plastics, polymers, insulating materials |
| Environmental Control | Controlled temperature and humidity |
| Voltage Source | DC voltage via megohmmeter or insulation tester |
| Result Output | Resistivity values (ohm/sq and ohm·cm) |
Instrumentation Used for Testing
- Megohmmeter or insulation resistance tester
- ASTM D257 electrode fixtures
- Environmental chambers for temperature and humidity control
- Calibrated resistance measurement systems
- Data acquisition and reporting software
Results and Deliverables
- Surface resistivity values
- Volume resistivity values
- Assessment of insulation performance
- Comparison of material resistivity characteristics
- Documentation supporting material selection and quality control
- Compliance verification for electrical safety requirements
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Read Case StudyFrequently Asked Questions
ASTM D257 is a test method for measuring electrical insulating materials' conductance, conductivity, volume, and surface resistivity.
ASTM D257 is a standard test method used for measuring the DC electrical resistivity or resistivity of insulating materials.
Surface resistivity measures the material's surface resistance to leakage current. On the other hand, volume resistivity measures the bulk material's resistance to current flow.
The higher the surface/volume resistivity, the lower the leakage current and the less conductive the material is.
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