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ISO 1209-1 Bending test for rigid cellular plastics

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ISO 1209-1 Rigid Cellular Plastics Flexural Properties Tester | UnitedTest

UnitedTest supplies ISO 1209-1 three-point bending test machines for rigid cellular plastics. This standard evaluates bending performance of rigid foam bars, measuring breaking load and load at specified deflection for quality control and material research.


ISO 1209‑1 Rigid cellular plastics — Determination of flexural properties — Part 1: Basic bending test

ISO 1209‑1 specifies a simple three‑point‑bending test to evaluate bending performance of rigid cellular plastic bar specimens. The test measures load at specified deflection or breaking load. It cannot calculate flexural strength or apparent flexural modulus, as small specimens fail to form a pure‑bending stress state; those mechanical parameters are defined under ISO 1209‑2. This standard applies only to foams with thickness ≥20 mm and is not valid for materials with obvious crushing during testing. UnitedTest manufactures reliable testing equipment complying with ISO 1209-1 for rigid cellular plastic flexural testing.


Test Principle

A rectangular specimen rests on two parallel support edges. A cylindrical loading edge applies a perpendicular compressive force at the mid‑span between supports at constant moving speed. The force value is recorded either when deflection reaches 20 mm, or at fracture (break) if rupture occurs before 20 mm deflection. It is a three‑point bending principle without pure‑bending condition.


Test Equipment required for ISO 1209-1 Bending test for rigid cellular plastics

Recommend UnitedTest Universal Testing Machine and Bending fixtures. 

Universal testing machine
movable cross‑head runs at constant speed; force measurement accuracy shall be ±1 % full‑scale range.
Three-point bending fixture

1. Two cylindrical support edges: radius (15 ± 1) mm, parallel, same horizontal plane; clear span between supports = 100 ± 1 mm. Support length exceeds specimen width.

2. Central loading edge: identical dimension and radius as supports, positioned centrally and parallel to two supports.

ISO 1209-1 Bending test for rigid cellular plastics

Dial‑gauge micrometerConforming to ISO 1923 for measuring specimen linear dimensions


Test Specimen Information

Shape/dimensions — rectangular parallelepiped (bar):

  • Length: (120 ± 1.20) mm

  • Width: (25 ± 0.25) mm

  • Thickness: (20 ± 0.20) mm

Preparation: cut without deforming the original cell structure. Specimens may retain a skin on one or more faces — this must be recorded.

Number of specimens:

  • Minimum 5 specimens per sample.

  • Suspected anisotropy → prepare duplicate sets with axes respectively parallel and normal to the suspected direction of anisotropy.

  • Single-surface skin specimens → test two sets, one with the skin in tension, one in compression; report separately.


Key Test Parameters: 

Support span100 ± 1 mm
Support & loading edge radius15 ± 1 mm
Loading (crosshead) speed10 ± 2 mm/min
Target deflection20 ± 0.2 mm
Load accuracy± 1 %
Specimens≥ 5 (more for anisotropic / skinned materials)
Conditioning≥ 6 h
Result unitsForce in newtons, deflection in mm
  1. This method cannot compute flexural strength or flexural modulus; use ISO 1209‑2 for modulus‑strength calculation.

  2. Not suitable for rigid cellular plastics exhibiting significant crushing deformation during bending.

  3. Material thickness shall not be less than 20 mm.


Details Test Procedures of ISO 1209-1 Bending test for rigid cellular plastics


  1. Measure specimen length, width, thickness following ISO 1923 requirements.

  2. Symmetrically mount specimen on supports; loading direction must be perpendicular to specimen longitudinal axis.

  3. Lower loading edge until light contact with specimen; set this point as zero‑deflection baseline.

  4. Drive loading edge downward at constant speed of 10 ± 2 mm/min.

  5. Record force in Newtons at deflection of 20 mm.

  6. If specimen fractures prior to reaching 20 mm deflection, capture breaking force and deflection‑at‑break.

  7. Collect data for all replicate specimens.


Test Application (Industry & Material Scope)


  • Building thermal insulation boards — XPS, EPS, PU/PIR, phenolic foam, cellulose foam (ISO 4898 Rigid cellular plastics — Thermal insulation products for buildings and ISO 21844 for cellulose foam are downstream product specs that rely on this family of methods).

  • Sandwich panel cores and structural/load-bearing foam cores.

  • Refrigeration & cold-chain insulation, LNG/cryogenic insulation (explains why −196 °C and −70 °C are listed as preferred test temperatures).

  • Automotive / transport, aerospace, marine and wind-energy foam cores.

  • Protective packaging and cushioning foams.

  • Routine QC / batch release, incoming-goods inspection, R&D formulation screening, and third-party certification testing.


Related Standard:

ASTM D790
Standard Test Methods for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials
ISO 14125Fibre-reinforced plastic composites -- Determination of flexural properties
ASTM D6272

Standard Test Method for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials by Four-Point Bending

ASTM D7264Standard Test Method for Flexural Properties of Polymer Matrix Composite Materials
ISO 178Plastics — Determination of flexural properties
GB/T 9341Equivalent to using ISO 178
JIS K 7171Japan standard Basically consistent with the technical content of ISO 178. (プラスチック-曲げ特性の求め方)
ISO 1209-1Rigid cellular plastics - Determination of flexural properties - Part 1: Basic bending test
ISO 1209‑2Companion part of the same series; determines flexural strength and apparent flexural modulus of elasticity for rigid cellular plastics (calculates formal flexural mechanical properties)
GB/T 8812.1Rigid cellular plastics - Determination of flexural properties - Part 1: Basic bending test
DIN 53423Germany corresponding bending test for rigid foams.
ASTM C203Standard Test Methods for Breaking Load and Flexural Properties of Block-Type Thermal Insulation, commonly used in North America as the functional counterpart for insulation boards.


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ISO 1209-1 rigid cellular plastics Electronic Universal Testing machine

WDW Series Computer Control Electronic Universal Testing Machine made by UNITEDTEST range from 100N to 600KN load capacity with various models like single columns, table type, door frame type etc., is used to perform tension, compression, flexure/bending, shearing, peeling etc., test for metal and nonmetal specimens. Matched with UNITEDTEST design and produced various test fixture, like peel, flexure, puncture, tear, pneumatic grip, belt tension etc., this UTM can be used to almost all materials include but not limited to steel rod, rubber, steel wire, plastic, seat belt, textile, wood, panel etc., mechanical performance inspection.

ISO 1209-1 cellular plastic mechanical test,foam flexural properties test

A single column tensile tester is a sophisticated material testing instrument designed for measuring mechanical properties of various materials under tension, compression, bending, shear, and other loading conditions. As the name suggests, it features a single vertical column supporting a moving crosshead that applies force to test specimens.

ISO 1209-1 cellular plastics laboratory tester,UnitedTest material testing machine

Three-point bending test fixture for fiber-reinforced plastic composites, designed in accordance with ISO 14125, provides a standardized method for determining the flexural properties of composite materials using a three-point bending test.

Related Standard

ASTM D790 Bending Test Flexural Properties of Unreinforced and Reinforced Plastics –

ASTM D790: Standard Test Methods for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials


ASTM D790 test methods are used to determine the flexural properties of unreinforced and reinforced plastics, including high modulus composites and electrical insulating materials utilizing a three-point loading system to apply a load to a simply supported beam (specimen). The method is generally applicable to both rigid and semi-rigid materials, but flexural strength cannot be determined for those materials that do not break or yield in the outer surface of the test specimen within the 5.0 % strain limit.

ISO 14125 Three points bending test of Fiber-Reinforced Plastic Composites –

ISO 14125 is a test method to determine flexure properties of fiber-reinforced plastic composites.

There are two methods used, Method A for a three-point flexure test and Method B for a four-point flexure test.

There are four material classes, Class I – IV, which define the specimen length, span, width, and thickness.

The standard requires deflection measurement not exceed +/- 1% error of full scale.


ISO 14125 is based on the ISO 178 standard and both utilize three point flexural testing of a freely supported bar loaded between the supports.

ISO 14125 focuses on fibre reinforced plastic compositesand has an alternative 4-point loading testing procedure, Procedure B.

The material properties recorded by following the standard are the flexural stress, flexural strain, elastic modulus in flexure and interlaminar shear modulus.

Compression-testing machine which will comply with ISO 5893 and shall be capable of maintaining speeds of (0.5 +- 20 %) mm/min to (500 +- 10 %) mm/min.

ISO 178 Plastics flexural / bending test –

ISO 178 Plastics - Determination of flexural properties

ISO 178 specifies a method for determining the flexural properties of rigid and semi-rigid plastics under defined conditions. A standard test specimen is defined, but parameters are included for alternative specimen sizes for use where appropriate. A range of test speeds is included.


ISO 178 test method is used to investigate the flexural behaviour of the test specimens and to determine the flexural strength, flexural modulus and other aspects of the flexural stress/strain relationship under the conditions defined. It applies to a freely supported beam, loaded at midspan (three-point loading test).

ISO 1209-2 Flexural Strength & Apparent Flexural Modulus Testing for Rigid Cellular Plastics –

ISO 1209-2 Rigid cellular plastics - Determination of flexural properties - Part 2: Determination of flexural strength and apparent flexural modulus of elasticity

ISO 1209-2 specifies a three-point bending test method to determine, on rigid cellular plastics: Flexural strength (R) — the maximum fibre stress the foam develops in bending; Apparent flexural modulus of elasticity (E) — the stiffness in bending.

The word "apparent" is deliberate: cellular plastics are not homogeneous continua — the measured stiffness includes shear deflection and local cell-wall crushing/indentation under the loading and support edges, so E is an engineering, configuration-dependent value, not a true material constant valid for all geometries.

ISO 1209‑1 Bending Test Frequently Asked Questions (FAQs)

Q1. What ISO 1209‑1 exactly does the test measure?

Two possible outputs, in newtons:

  • the force at 20 mm deflection, or

  • the breaking force plus the deflection at break (if the specimen breaks before reaching 20 mm).



Q2. Why is bending performance important for rigid foams?

In service, insulation boards and foam cores are loaded in flexure, not pure tension or compression — during handling, transport, installation, foot traffic, wind load and thermal cycling. A foam with good compressive strength can still crack or snap in bending. This test reproduces that failure mode directly.


Q3. Can I report "bending strength in MPa" from ISO 1209-1?

No. The standard states this explicitly: because it uses small specimens and does not produce pure bending, the method does not permit calculation of flexural strength or apparent flexural modulus of elasticity. For those values you must use ISO 1209-2. Reporting Part-1 loads as "strength" is the single most common misuse of this standard.


Q4. Why is it called the "basic" bending test?

Because it is the simplified screening tier of a two-part series: Part 1 gives comparative load/deflection data quickly and cheaply; Part 2 gives true engineering properties (flexural strength and apparent modulus) using larger specimens, a longer span and a recorded force–deflection curve.


Q5. Which materials can be tested?

Rigid cellular plastics — e.g. XPS, EPS, PU/PIR, phenolic and cellulose foam boards, sandwich panel cores, packaging foams — ≥ 20 mm thick. It is not applicable to materials showing significant crushing, and results are only comparable between materials of similar physical properties and dimensions.


Q6. Why test skins in both tension and compression?

Cellular plastics are highly skin- and orientation-sensitive: a board with a skin on one side behaves very differently depending on whether that skin is stretched or compressed. Testing both orientations, and reporting separately, exposes weaknesses a "homogeneous material" assumption would hide.


Q7. What does the precision data tell me?

From a 1993 interlaboratory trial (10 laboratories, 4 products, analysed per ISO 5725), at the 95 % confidence level: repeatability limit ≈ 5 % and reproducibility limit ≈ 15 %. So treat small differences between labs with caution, and always report the mean and standard deviation of at least five results.


Q8. What industries require it?

Building thermal insulation (XPS/EPS/PU/PIR/phenolic, per specs such as ISO 4898), sandwich panel cores, refrigeration and cold-chain/LNG insulation, automotive, aerospace, marine and wind-energy cores, protective packaging, plus routine QC, incoming inspection, R&D screening and third-party certification labs.


Q9. ISO 1209-1 vs ISO 1209-2 — which one do I need?

Use Part 1 for fast, comparative, cost-effective screening (load at 20 mm deflection or breaking load) on small specimens. Use Part 2 when you need genuine design data — flexural strength and apparent flexural modulus — from a recorded force–deflection curve with a longer span (recommended 300 mm) and higher speed (20 ± 1 mm/min). Many labs run Part 1 for production QC and Part 2 for material qualification.


Q10: Why cannot ISO 1209‑1 calculate flexural strength?

The fixture and small‑specimen setup do not create pure‑bending stress state. Significant shear deformation occurs inside the foam, so standard flexural‑strength formulas are invalid for ISO 1209‑1 test data.


Q11: Can I use ISO 178 (general‑plastic flexural test) instead of ISO 1209‑1 for rigid foam?

Not recommended. ISO 178 is designed for solid plastics and explicitly states it is unsuitable for rigid cellular foams. Foam’s porous cell structure requires dedicated ISO 1209‑1 / ISO 1209‑2 fixtures and specimen rules.


Q12: Why choose ISO 1209‑1 Rigid Cellular Plastics Basic Bending Test Machine & Fixture from UnitedTest?

UnitedTest supplies ISO 1209‑1 three‑point bending test fixtures and universal testing machines for rigid cellular plastics / rigid foams. Meet ISO 1209‑1:2007 standard for basic bending test of rigid foam insulation, XPS, EPS, PU foam.


UnitedTest provides complete mechanical testing solutions for ISO 1209‑1:2007 Rigid cellular plastics — Determination of flexural properties — Part 1: Basic bending test. Our universal testing machines with dedicated three‑point bending fixtures are built to comply fully with ISO 1209‑1 requirements for rigid foam bending screening tests.

ISO 1209‑1 is the widely‑adopted international three‑point‑bending test for rigid cellular plastics including rigid PU foam, XPS extruded polystyrene, EPS expanded polystyrene and phenolic rigid foam. It is used in building insulation manufacturing, cold‑chain insulation industry, protective foam packaging and lightweight transport‑component quality‑control laboratories. The test measures load at specified deflection or breaking load for material comparison and batch screening.


UnitedTest ISO 1209‑1 test fixture key specifications:

  • Cylindrical loading edge and support rollers: radius 15 ± 1 mm

  • Fixed support span: 100 ± 1 mm for ISO 1209‑1 specimen size (120 × 25 × 20 mm)

  • Fixture width fits standard 25 mm‑width rigid‑foam test bars

  • Compatible with UnitedTest computer‑controlled universal tensile‑testing machines, adjustable cross‑head speed from 10 ± 2 mm/min as required by ISO 1209‑1

  • Force‑measurement accuracy up to ± 1 %, meets standard metrology requirement

  • Supports automatic recording force‑deflection curve, force at 20 mm deflection and break‑load data output

Important note: ISO 1209‑1 delivers raw force data only. When you need flexural strength and apparent flexural modulus calculation for engineering design, UnitedTest also supports ISO 1209‑2 test configuration for rigid cellular plastics.

Our test system helps QC labs, foam material R&D centres and third‑party testing laboratories achieve repeatable ISO 1209‑1 test results, for incoming‑material inspection, production batch release, new‑formula development and third‑party certification tests.

Contact UnitedTest’s application‑engineering team for your ISO 1209‑1 rigid‑foam bending‑test setup, load‑range selection, fixture customisation and complete testing‑lab solution.

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