Hardness Rockwell M
Last update on Jul 11, 2025
Rockwell hardness M scale is important in plastics evaluation because it's specifically designed for testing medium-hard polymers. This scale uses a larger ball indenter (1/4 inch) and lower test load (100 kg) than Rockwell R, making it ideal for measuring materials that would bottom out on softer scales but aren't hard enough for reliable readings on scales used for rigid plastics.
In this guide, we will provide you Rockwell M values that are crucial for quality control, material comparison, and specification compliance, particularly for acetal, nylon, polycarbonate, and other important engineering polymers.
What is Rockwell M hardness of plastics?
Rockwell hardness test is one possible method to measure the hardness of plastics. This test method is named after Stanley P. Rockwell, who invented it in 1914. It is generally used for hard materials, like:
Here, the resilience or creep of the polymer is less likely to affect results. For rubbers, elastomers, and softer plastics, shore hardness is often preferred.
Principle of Rockwell hardness scale
The Rockwell scale determines the hardness by measuring the depth of penetration of an indenter. This happens under a large load compared to the indentation made by a pre-load. Different scales use varied loads or indenters such as:
- diamond tips,
- steel, or
- tungsten carbide balls.
The result is a dimensionless number. There are different scales that are denoted by a single letter. The three most common scales used for testing the hardness of plastics are Rockwell E, Rockwell M, and Rockwell R.
Which factors influence the Rockwell M hardness of materials?
As the method is extended from metals to plastics, one must be careful to consider:
- Type of plastics
Different plastics have varied hardness levels. For example, PA is generally harder than polyethylene (PE). Thus, a PA sample will have a higher Rockwell M hardness than a PE sample of the same thickness.
- Thickness of the material
The Rockwell M hardness test is not valid for plastics that are less than 0.05 inch (1.27 mm) thick. This is because the indenter can penetrate too deeply into thin materials, giving a falsely high hardness reading.
- Temperature
Small changes in temperature can result in first and second-order phase transitions. This can alter the hardness of the material.
- Viscoelasticity
Unlike metals, plastics are viscoelastic. Stress-strain relationships are time-dependent. The results obtained by dragging the weighted indenter will be rate-dependent.
- Surface finish
The surface finish of the plastics can affect the Rockwell M hardness reading. A rough surface can cause the indenter to dig in more deeply, giving a falsely high hardness reading.
What are the advantages of Rockwell M hardness?
- The Rockwell M hardness test is used to measure the hardness of a wide range of materials. For example, metals, plastics, ceramics, and composite materials (such as fiberglass and carbon fiber).
- It ensures the meeting of the required quality standards of the materials.
- It helps to monitor the progress of a manufacturing process and ensure that the desired hardness is being achieved.
- It can be used to identify the cause of a failure in a material.
- It enables to study the effects of different factors on the hardness of a material. For example, a researcher may use the Rockwell M hardness test to study the effects of heat treatment on the hardness of acrylonitrile butadiene styrene (ABS) plastics.
Which test methods measure the Rockwell M hardness of plastics?
- ASTM D785 — It determines the Rockwell hardness of plastics and electrical insulating materials.
- ISO2039-2 — It determines the hardness of plastics.
- Part 2: Determines the Rockwell hardness.
- Part 2: Determines the Rockwell hardness.
Rockwell Hardness Test Method (Source: MaterialsScience2000)
What are the Rockwell M hardness values for various plastics?
Click to find the polymer you are looking for:
| Polymer Name | Min Value | Max Value |
| ABS Flame Retardant | 20.00 | 70.00 |
| ABS High Heat | 20.00 | 50.00 |
| ABS High Impact | 10.00 | 30.00 |
| ABS/PC Blend - Acrylonitrile Butadiene Styrene/Polycarbonate Blend | 50.00 | 70.00 |
| ABS/PC Blend 20% Glass Fiber | 50.00 | 80.00 |
| ABS/PC Flame Retardant | 50.00 | 80.00 |
| Amorphous TPI Blend, Ultra-high heat, Chemical Resistant (Standard Flow) | 112.00 | 112.00 |
| ASA - Acrylonitrile Styrene Acrylate | 10.00 | 20.0 |
| ASA/PC Blend - Acrylonitrile Styrene Acrylate/Polycarbonate Blend | 30.00 | 60.00 |
| ASA/PC Flame Retardant | 30.00 | 70.00 |
| ASA/PVC Blend - Acrylonitrile Styrene Acrylate/Polyvinyl Chloride Blend | 30.00 | 70.00 |
| CA - Cellulose Acetate | 1.00 | 80.00 |
| CAB - Cellulose Acetate Butyrate | 1.00 | 70.00 |
| CP - Cellulose Proprionate | 1.00 | 75.00 |
| CPVC - Chlorinated Polyvinyl Chloride | 40.00 | 65.00 |
| ETFE - Ethylene Tetrafluoroethylene | 1.00 | 10.00 |
| EVA - Ethylene Vinyl Acetate | 1.00 | 1.00 |
| EVOH - Ethylene Vinyl Alcohol | 85.00 | 104.00 |
| FEP - Fluorinated Ethylene Propylene | 1.00 | 1.00 |
| HDPE - High Density Polyethylene | 1.00 | 1.00 |
| HIPS - High Impact Polystyrene | 1.00 | 1.00 |
| HIPS Flame Retardant V0 | 1.00 | 1.00 |
| Ionomer (Ethylene-Methyl Acrylate Copolymer) | 1.00 | 1.00 |
| LCP - Liquid Crystal Polymer | 40.00 | 76.0 |
| LCP Carbon Fiber-reinforced | 99.00 | 99.0 |
| LCP Glass Fiber-reinforced | 77.00 | 87.0 |
| LCP Mineral-filled | 63.00 | 79.0 |
| LDPE - Low Density Polyethylene | 1.00 | 1.00 |
| LLDPE - Linear Low Density Polyethylene | 1.00 | 1.00 |
| PA 11 - (Polyamide 11) 30% Glass fiber reinforced | 116.00 | 116.00 |
| PA 11, Rigid | 1.00 | 25.00 |
| PA 12 (Polyamide 12), Glass Filled | 107.00 | 107.00 |
| PA 46 - Polyamide 46 | 92.00 | 92.00 |
| PA 6 - Polyamide 6 | 30.00 | 80.00 |
| PA 6-10 - Polyamide 6-10 | 1.00 | 50.00 |
| PA 66 - Polyamide 6-6 | 30.00 | 80.00 |
| PA 66, 30% Glass Fiber | 30.00 | 80.00 |
| PA 66, 30% Mineral filled | 30.00 | 80.00 |
| PA 66, Impact Modified, 15-30% Glass Fiber | 66.00 | 96.00 |
| PA 66, Impact Modified | 50.00 | 94.00 |
| PAI - Polyamide-Imide | 105.00 | 120.00 |
| PAI, 30% Glass Fiber | 95.00 | 110.00 |
| PAI, Low Friction | 95.00 | 110.00 |
| PAN - Polyacrylonitrile | 45.00 | 78.00 |
| PARA (Polyarylamide), 30-60% glass fiber | 110.00 | 110.00 |
| PBT - Polybutylene Terephthalate | 70.00 | 90.00 |
| PBT, 30% Glass Fiber | 90.00 | 95.00 |
| PC (Polycarbonate) 20-40% Glass Fiber | 70.00 | 95.00 |
| PC (Polycarbonate) 20-40% Glass Fiber Flame Retardant | 70.00 | 95.00 |
| PC - Polycarbonate, high heat | 70.00 | 90.00 |
| PCTFE - Polymonochlorotrifluoroethylene | 10.00 | 40 |
| PE - Polyethylene 30% Glass Fiber | 1.00 | 20.00 |
| PEEK - Polyetheretherketone | 55.00 | 100.00 |
| PEEK 30% Carbon Fiber-reinforced | 70.00 | 107.00 |
| PEEK 30% Glass Fiber-reinforced | 70.00 | 103.00 |
| PEI - Polyetherimide | 100.00 | 110.00 |
| PEI, 30% Glass Fiber-reinforced | 90.00 | 125.00 |
| PEI, Mineral Filled | 90.00 | 120.00 |
| PESU - Polyethersulfone | 85.00 | 88.00 |
| PESU 10-30% glass fiber | 90.00 | 99.00 |
| PET - Polyethylene Terephthalate | 50.00 | 100.00 |
| PET, 30% Glass Fiber-reinforced | 70.00 | 95.00 |
| PET, 30/35% Glass Fiber-reinforced, Impact Modified | 62.00 | 62.00 |
| PE-UHMW | 1.00 | 1.00 |
| PFA - Perfluoroalkoxy | 1.00 | 1.00 |
| PI - Polyimide | 110.00 | 110.00 |
| PMMA - Polymethylmethacrylate/Acrylic | 70.00 | 105.00 |
| PMMA (Acrylic) High Heat | 90.00 | 100.00 |
| PMMA (Acrylic) Impact Modified | 35.00 | 80.00 |
| PMP - Polymethylpentene | 100.00 | 100.00 |
| PMP 30% Glass Fiber-reinforced | 1.00 | 20.00 |
| PMP Mineral Filled | 1.00 | 20.00 |
| POM - Polyoxymethylene (Acetal) | 75.00 | 94.00 |
| POM (Acetal) Impact Modified | 35.00 | 79.00 |
| POM (Acetal) Low Friction | 58.00 | 94.00 |
| POM (Acetal) Mineral Filled | 83.00 | 90.00 |
| PP - Polypropylene 10-20% Glass Fiber | 20.00 | 50.00 |
| PP, 10-40% Mineral Filled | 1.00 | 20.00 |
| PP, 10-40% Talc Filled | 10.00 | 45.00 |
| PP, 30-40% Glass Fiber-reinforced | 40.00 | 50.00 |
| PP (Polypropylene) Copolymer | 1.00 | 20.00 |
| PP (Polypropylene) Homopolymer | 1.00 | 30.00 |
| PP, Impact Modified | 1.00 | 1.00 |
| PPA - Polyphthalamide, 33% Glass Fiber-reinforced | 124.00 | 126.00 |
| PPA, 45% Glass Fiber-reinforced | 124.00 | 126.00 |
| PPE - Polyphenylene Ether | 50.00 | 70.00 |
| PPE, 30% Glass Fiber-reinforced | 50.00 | 70.00 |
| PPE, Flame Retardant | 50.00 | 70.00 |
| PPE, Impact Modified | 50.00 | 70.00 |
| PPE, Mineral Filled | 60.00 | 70.00 |
| PPS - Polyphenylene Sulfide | 70.00 | 85.00 |
| PPS, 20-30% Glass fiber | 80.00 | 103.00 |
| PPS, 40% Glass fiber | 100.00 | 104.00 |
| PPS, conductive | 70.00 | 100.00 |
| PPS, Glass fiber & mineral | 66.00 | 102.00 |
| PPSU - Polyphenylene Sulfone | 80.00 | 80.00 |
| PS (Polystyrene) 30% glass fiber | 80.00 | 91.00 |
| PS (Polystyrene) Crystal | 60.00 | 75.00 |
| PS, High Heat | 75.00 | 85.00 |
| PSU - Polysulfone | 69.00 | 91.00 |
| PSU, 30% Glass fiber-reinforced | 87.00 | 100.00 |
| PSU Mineral Filled | 70.00 | 74.00 |
| PTFE - Polytetrafluoroethylene | 1.00 | 1.00 |
| PTFE, 25% Glass Fiber-reinforced | 1.00 | 1.00 |
| PVC (Polyvinyl Chloride), 20% Glass Fiber-reinforced | 50.00 | 70.00 |
| PVC, Plasticized | 1.00 | 1.00 |
| PVC, Plasticized Filled | 1.00 | 1.00 |
| PVC Rigid | 1.00 | 70.00 |
| PVDC - Polyvinylidene Chloride | 60.00 | 65.00 |
| PVDF - Polyvinylidene Fluoride | 75.00 | 75.00 |
| SAN - Styrene Acrylonitrile | 10.00 | 80.00 |
| SAN, 20% Glass Fiber-reinforced | 80.00 | 100.00 |
| SMA - Styrene Maleic Anhydride | 30.00 | 40.00 |
| SMA, 20% Glass Fiber-reinforced | 30.00 | 40.00 |
| SMA, Flame Retardant V0 | 30.00 | 40.00 |
| SMMA - Styrene Methyl Methacrylate | 65.00 | 75.00 |
| XLPE - Crosslinked Polyethylene | 1.00 | 20.00 |