ISO 48-2:2018 describes IRHD hardness testing for vulcanized and thermoplastic rubber, covering hardness values from 10 IRHD to 100 IRHD. It includes multiple instrument/method options for standard hardness on flat surfaces and apparent hardness when the test surface or part geometry is curved.
If you need help choosing the right IRHD method (normal, high, low, or micro) for your sample thickness, part shape, and target hardness range, talk with our team about aligning the setup to the exact edition you are working to.
ISO 48-2:2018 — Rubber, vulcanized or thermoplastic — Determination of hardness — Part 2: Hardness between 10 IRHD and 100 IRHD
ISO 48-2 is an International Standard for measuring rubber hardness using the International Rubber Hardness Degrees (IRHD) scale. It supports both routine hardness checks on flat test pieces and “apparent hardness” measurements when real parts (such as curved items) must be tested.
This standard focuses on ball-indentation style hardness measurement, with method choices primarily differentiated by indenter ball size and applied force to suit different hardness ranges and sample constraints.
Quick Definition
What it is: A rubber hardness test standard using IRHD, covering 10 to 100 IRHD.
What it measures: Indentation-based hardness reported in IRHD, including standard hardness (flat, standard test pieces) and apparent hardness (curved surfaces or non-standard geometry).
What it is not: It does not cover pocket hardness meter testing; that approach is addressed in ISO 48-5.
What This Standard Covers
ISO 48-2 specifies four “standard hardness” methods for flat surfaces and four related “apparent hardness” methods for curved surfaces. The methods are selected based on the expected hardness level and practical sample limitations (such as thickness, lateral size, and curvature).
| Method | Common use within ISO 48-2 | Hardness range guidance (IRHD) |
|---|---|---|
| N | Normal test for standard hardness on flat surfaces | Appropriate 35–85 (also used 30–95) |
| H | High-hardness test for standard hardness on flat surfaces | Appropriate 85–100 |
| L | Low-hardness test for standard hardness on flat surfaces | Appropriate 10–35 |
| M | Microtest (scaled-down normal test) for thinner/smaller pieces | Appropriate 35–85 (also used 30–95) |
For curved surfaces, ISO 48-2 also defines apparent-hardness variants (CN, CH, CL, and CM) that correspond to the N, H, L, and M methods. It also allows apparent hardness reporting on non-standard flat test pieces when the standard test-piece geometry cannot be met.
Why This Standard Matters in Testing
IRHD hardness is widely used as a fast, production-friendly indicator of rubber stiffness and consistency. ISO 48-2 gives a controlled, instrumented approach to indentation hardness so results can be compared across lots, suppliers, and laboratories using a consistent method definition and reporting format.
Because the standard includes multiple methods (and curved-surface variants), matching the method to the expected hardness level and part geometry is important for meaningful comparisons—especially when a drawing, procurement document, or customer specification cites a particular ISO 48-2 method.
Common Materials, Product Types, or Applications Covered
ISO 48-2 applies to vulcanized rubber and thermoplastic rubber materials where indentation hardness in IRHD is needed. It is commonly used for:
- Flat rubber sheets, plaques, and molded test pieces used for QC and material release
- Finished rubber parts where hardness must be checked directly on the article
- Curved components (for example, rings and other curved profiles) where “apparent hardness” is more practical than preparing standard flat test pieces
When the part shape or thickness cannot meet standard test-piece requirements, the standard’s apparent-hardness approach can be used to produce a controlled, documented hardness value that reflects the real part geometry.
Common Test or Verification Workflow
In day-to-day lab and production use, ISO 48-2 is often part of a material verification workflow that checks incoming material, in-process conditions, or finished goods against hardness targets.
Common workflow: Select the appropriate method (N, H, L, or M) for the expected hardness and sample constraints → condition and support the test piece appropriately → make IRHD measurements on the required surface type (flat standard hardness or curved apparent hardness) → report hardness in IRHD with the method and any geometry constraints clearly stated.
Reporting sensitivity: Hardness results and comparability depend on using the intended ISO 48-2 method and properly identifying whether the value is standard hardness or apparent hardness.
Equipment Commonly Used for This Standard
ISO 48-2 typically points to an IRHD hardness tester capable of ball-indentation measurements with the force/indenter configurations needed for the chosen method (N, H, L, or M). For curved parts, the setup may also require stable supports or fixtures so the instrument and test piece are properly seated during the measurement.
Common equipment: IRHD hardness tester (normal/high/low and/or micro capability as required), appropriate anvils/supports for flat testing, and part supports/fixtures for curved apparent-hardness testing.
If you are selecting an IRHD system for production or lab use—especially when you need both standard hardness on flat pieces and apparent hardness on real parts—you can request a detailed quote for an instrument configuration matched to the hardness range and sample geometry you run.
How to Read This Designation or Revision
ISO 48-2 indicates Part 2 of the ISO 48 series for rubber hardness determination. The “:2018” year identifies the published edition of the document.
ISO 48-2:2018 replaced ISO 48:2010; when a customer requirement cites “ISO 48” without the part number, it is important to confirm whether they mean the older ISO 48:2010 document or the newer ISO 48-2 structure.
Related Standards, Methods, or Frameworks
Depending on what your customer specification is trying to control, related references commonly used alongside ISO 48-2 include:
- ISO 48-1 (guide to hardness testing within the ISO 48 series)
- ISO 48-5 (pocket hardness meter approach, which ISO 48-2 explicitly excludes)
- ISO 48-6 / ISO 48-7 / ISO 48-8 (IRHD approaches for rubber-covered rollers, handled outside ISO 48-2)
- ISO 48-9 (calibration and verification of hardness testers within the ISO 48 series)
- ISO 23529 (general procedures for preparing and conditioning rubber test pieces for physical testing)
When contracts or drawings reference multiple hardness standards (for example, IRHD and Shore scales), it’s good practice to align on the required method and reporting units before testing begins.
Talk with us about ISO 48-2 equipment and setup
If you’re planning an ISO 48-2 hardness testing workflow for flat test pieces, curved parts, or both, contact our team to discuss method selection (N/H/L/M vs. curved variants), fixture needs, and tester configuration for your target IRHD range.