Concora Medium (CMT)

Corrugated medium testing is a key process in the packaging industry, ensuring that materials used in box and carton production meet strict durability and performance standards. As supply chains expand and consumer expectations increase, packaging must withstand handling, stacking, and transport stresses without loss of structural integrity.

At the centre of this testing is the measurement of crush resistance in the corrugated medium - the fluted inner layer between linerboards that gives corrugated board its strength. This testing provides manufacturers and quality control engineers with vital data to identify weaknesses, ensure compliance with industry standards, and maintain consistent quality in production.

By safeguarding the reliability of packaging materials, corrugated medium testing helps to protect goods from damage, minimise waste, and reduce costs across the supply chain.

TAPPI T 809 is an internationally recognised method for determining the flat crush resistance of corrugated medium. Published by the Technical Association of the Pulp and Paper Industry, it sets out a controlled procedure for evaluating a medium's resistance to compressive forces applied perpendicular to its surface.

The method is significant because crush strength is directly linked to packaging performance under real-world storage and transport conditions. Materials that achieve higher flat crush values in TAPPI T 809 testing generally perform better in stacked loads or under top-load pressure.

Key features of TAPPI T 809 include:

• Precise specimen preparation to avoid irregularities affecting results
• Controlled compression speed for repeatable testing
• Defined test parameters and reporting requirements for quality assurance

By applying this standard, manufacturers can maintain production consistency and meet both regulatory and client-specific packaging requirements.

The flat crush test, also known as the Concora Medium Test (CMT), measures the maximum force a corrugated medium can withstand before flute collapse. In CMT testing, the medium is first formed into flutes using a laboratory fluter before testing. The result is a direct indicator of a material's ability to resist crushing forces and maintain its structure within a finished box.

Purpose of the test

• Assess the strength of fluting in corrugated medium
• Predict board performance under top-load or stacking conditions
• Support material selection and process optimisation for packaging design

Specimen types

• A, B, and C flute mediums in various grammages
• Mediums conditioned at different moisture levels to simulate storage environments
• Samples from single-wall, double-wall, and triple-wall constructions where relevant

Typical test parameters

• Specimen size: 152.4 mm square
• Conditioning: 23°C ± 1°C, 50% ± 2% relative humidity
• Compression rate: 12.5 mm/min
• Force measurement accuracy: to 0.1 N

A flat crush tester comprises two smooth, parallel platens, one fixed and one moving under controlled load application. The conditioned specimen is placed between the platens with flutes oriented vertically. Force is applied until the flutes collapse, and the peak force is recorded as the flat crush value.

Accurate results depend on:

• Calibrated load cells
• Verified platen parallelism
• Adherence to the compression speed specified in TAPPI T 809

CMT testing offers multiple operational and commercial advantages:

• Enhanced durability - Ensures packaging withstands handling and stacking stresses
• Improved quality control - Identifies material defects before mass production
• Material efficiency - Enables optimisation of raw material use without reducing performance
• Reduced transport damage - Minimises product loss, returns, and associated costs

For example, a manufacturer that switched from a lower-grade medium to one with a CMT value around 15 percent higher reported a measurable reduction in transit-related damage, lowering warranty claims and improving customer satisfaction.

• Prepare the specimen - Cut to size with clean edges, ensuring flutes remain undamaged, and condition as per the standard.
• Calibrate the equipment - Check the load cell and platen alignment.
• Position the specimen - Place between platens with flutes vertical.
• Apply force - Compress at the specified rate until flute collapse.
• Interpret results - Compare peak force to specification requirements and note any localised failures.
• Record and report - Document results with specimen details, environmental conditions, and equipment settings.

Heavy industrial packaging - A manufacturer supplying boxes for machine components integrated routine CMT testing to track performance trends. By selecting an optimal flute profile, they maintained crush strength while reducing material weight by 8 percent.

E-commerce packaging - An online retailer experiencing carton damage found that their medium stock underperformed in CMT testing. Switching to a higher-grade medium improved crush strength by around 20 percent and reduced returns.

These examples demonstrate how integrating CMT testing into quality control processes can drive measurable performance and cost benefits.

Mecmesin offers flat crush testers and fixtures designed to meet TAPPI T 809 requirements. Our OmniTest and MultiTest-dV motorised test stands, combined with VectorPro software, provide:

• High-precision load measurement to 0.1 N
• Depth resolution to 0.01 mm
• Programmable test speeds for full standard compliance
• Automated data capture, analysis, and reporting for traceability

Whether for R&D, production quality checks, or supplier verification, Mecmesin systems deliver repeatable, reliable results for corrugated medium testing.

Corrugated medium testing, and particularly the flat crush test under TAPPI T 809, is essential for ensuring packaging strength, reliability, and compliance. Using accurate, calibrated Mecmesin systems and following best practice procedures allows manufacturers to improve product performance, reduce costs, and enhance customer satisfaction.

For advice on selecting equipment, setting up tests, or meeting TAPPI T 809 requirements, speak to Mecmesin’s technical team. Our consultative approach ensures you receive the right solution for your testing needs.