ASTM D395 is a set of test methods used to measure compression set in rubber—how well an elastomer rebounds after being held under compressive stress for a defined time, typically at an elevated temperature.
It is widely used for seals, gaskets, mounts, vibration dampers, and other rubber components where long-term sealing force or resilience matters. If you need help selecting the right method (A, B, or C) for your material and service conditions, talk with our team.
ASTM D395: Standard Test Methods for Rubber Property—Compression Set
ASTM D395 defines standardized approaches for evaluating how rubber materials retain elastic recovery after prolonged compressive loading. In many product specifications, compression set limits are used as acceptance criteria for parts that must maintain contact pressure over time (for example, sealing and vibration isolation components).
The standard includes multiple test methods because rubber parts can be stressed in different ways in service (for example, held at a fixed deflection versus loaded by a defined force), and the method selection can affect how results correlate to real use.
Quick definition
Compression set: A measure of permanent deformation (loss of thickness recovery) after a rubber specimen has been compressed for a specified duration and then allowed to recover.
What ASTM D395 provides: Standardized test method options (A, B, and C) for generating comparable compression set values for rubber materials tested in air or liquid media.
What This Standard Covers
ASTM D395 applies to rubber intended for applications where the material is subjected to compressive stresses in air or in a liquid environment. It is commonly applied to rubber used in machinery mountings, vibration dampers, and seals.
Test methods included in ASTM D395: Method A (constant force in air), Method B (constant deflection in air), and Method C (constant deflection in air with consideration of material hardness).
Method selection note: Unless a detailed product specification states otherwise, Method B is commonly used. ASTM D395 also notes that Method B is not suitable for vulcanizates harder than 90 IRHD.
Why This Standard Matters in Testing
Compression set is often used to screen materials and qualify compounds for long-duration static compression conditions, especially when heat exposure is involved. For many sealing and isolation parts, a lower compression set generally supports better retention of sealing force or preload over time.
Because compression set is sensitive to method choice, time, temperature, specimen geometry, and recovery measurement, it is important that quotes, compliance reports, and supplier PPAP/FAI packages align to the exact ASTM D395 method and the exact conditioning requirements called out by the drawing or procurement specification.
Common Materials, Product Types, or Applications Covered
ASTM D395 is most commonly associated with vulcanized rubber and elastomer compounds used in components that see sustained compression.
Common products: O-rings, molded seals, gaskets, compression seals, bushings, machinery mounts, vibration isolators, and dampers.
Common industries: Automotive, industrial equipment, fluid handling, pumps/valves, HVAC, and general sealing applications where durability under heat and compression is a key requirement.
Common Test or Verification Workflow
Compression set testing is typically used in material qualification and incoming/lot acceptance where a specification requires demonstrating elastic recovery after a defined compressive exposure.
Typical workflow: Prepare specimens (often from molded slabs or representative parts) → apply compression using the selected ASTM D395 method (A, B, or C) for a defined time and temperature → allow the specimen to recover per the method → measure thickness change and report compression set.
Key practical control points: method selection (A/B/C), deflection or force control approach, temperature uniformity, exposure duration, recovery timing, and repeatable thickness measurement.
Equipment Commonly Used for This Standard
ASTM D395 is most directly tied to compression set fixtures and controlled thermal exposure equipment. The method choice influences whether you need constant-force loading capability or a constant-deflection compression device.
Common equipment: Compression set fixtures (constant deflection jigs and spacers), deadweight or force-controlled compression hardware (for constant-force work), thickness measurement tools (gauges/micrometers suited to rubber), and temperature-controlled ovens for air aging.
When liquid media is specified: A compatible temperature-controlled bath and containers/holders may be required to maintain exposure conditions without damaging the fixture or contaminating the medium.
If you are comparing fixture styles, specimen sizes, or oven/bath temperature ranges for your ASTM D395 setup, you can request a detailed quote matched to the method and throughput you need.
How to Read This Designation or Revision
ASTM standards are cited by designation and revision status. ASTM D395 may be referenced with a year and, in some cases, a reapproval marker.
Example designation format seen in procurement: ASTM D395-18R25.
What it generally indicates: “D395” is the standard number; “-18” indicates the edition originally issued or last revised in 2018; “R25” indicates a reapproval in 2025. Because requirements and method details can change between editions, test setup and reporting should follow the exact cited version on the drawing or specification.
Related Standards, Methods, or Frameworks when useful
Compression set is one part of a broader rubber test plan. Many specifications pair compression set with other property checks (for example, tensile, hardness, or fluid exposure) depending on the service environment.
Related example: For compression set requirements at low temperatures, some specifications may cite ASTM D1229 (a separate ASTM test method focused on low-temperature compression set behavior).
Get help selecting an ASTM D395 test setup
For quoting or procurement, the fastest way to align equipment and fixtures is to confirm the method (A, B, or C), the exposure temperature range, and whether testing is in air or liquid media. To review your requirement and match the right configuration, request pricing for an ASTM D395-capable setup.