Mattress firmness testing objectively measures the load-bearing characteristics of sleep surfaces, enabling manufacturers to grade comfort, verify performance claims, and demonstrate compliance with international standards. Using standardized indentation methods such as EN 1957, ASTM F1566, and ISO 2439, accredited third-party laboratories quantify hardness values, firmness ratings, and firmness loss for innerspring, foam, latex, and hybrid mattresses. This technical article explains the principal test methods, sample requirements, measured parameters, and practical applications of mattress hardness testing.
Technical Overview
Mattress firmness, also referred to as mattress hardness, describes the resistance a sleep surface offers when it is compressed by an applied load. It is a function of the core construction, spring gauge and geometry, foam density and formulation, quilting layers, and overall thickness. Because firmness directly influences perceived comfort, spinal alignment, pressure distribution, and long-term performance, it is one of the most frequently specified parameters in product datasheets, procurement contracts, and regulatory frameworks.
Firmness cannot be reliably assessed by subjective lying trials alone. Standardized indentation testing applies controlled forces through a defined loading pad and records the resulting deflection, producing repeatable, instrument-measured values that can be compared across products, production batches, and suppliers. The principal frameworks used by accredited third-party laboratories include:
- EN 1957 — European test method for determining the firmness of mattresses and mattress pads
- ASTM F1566 and ASTM F1857 — North American performance test methods and specifications for innerspring, hybrid, and boxspring mattresses and foundations
- ASTM D3574 and ISO 2439 — component-level indentation hardness of flexible polyurethane and latex foams
- GB/T 26706 and QB/T 1952.2 — Chinese national and industry standards covering palm-fibre elastic mattresses and spring soft mattresses
- AS/NZS 8811.1.3 — firmness test method for infant sleep surfaces, complemented by the safety provisions of ASTM F2933 for crib mattresses
Testing is typically performed by ISO/IEC 17025-accredited third-party laboratories, which ensures calibrated instrumentation, traceable measurement, and internationally recognized reporting for quality control, product certification, and market surveillance purposes.
Testing Samples
Innerspring and Hybrid Mattresses
Complete production units of pocket-spring, bonnell, continuous-coil, and hybrid constructions are tested in their finished configuration, including comfort layers and quilted covers, since all components contribute to the measured firmness response.
Foam, Memory Foam, and Latex Mattresses
All-foam and latex mattresses are tested as complete units, while raw foam cores and comfort layers may additionally be evaluated as cut components under foam-specific hardness standards to support material qualification and incoming inspection.
Palm-Fibre and Specialty Mattresses
Coconut-fibre and palm-fibre elastic mattresses, which are widely specified under Chinese standards, are tested for hardness classification along with durability and hygiene parameters defined by the applicable national and industry standards.
Mattress Pads, Toppers, and Infant Mattresses
Thin mattress toppers are evaluated for firmness contribution when placed on a defined rigid substrate, while crib and infant mattresses are subjected to dedicated sleep-surface firmness requirements due to the safety-critical nature of these products.
Prior to testing, samples are conditioned in a controlled standard atmosphere, typically 23 ± 2 °C and 50 ± 5 % relative humidity, for a minimum of 24 hours to stabilize cell structure and spring behavior. Firmness evaluation is generally non-destructive, but durability-related firmness retention testing requires dedicated units, as it permanently alters the specimen.
Testing Items
Depending on the selected standard and the purpose of the evaluation, a mattress firmness testing program may include the following measured parameters:
- Initial firmness (hardness) value H, expressed in N/mm, derived from the force–deflection characteristic
- Firmness rating classification on the standardized 1 to 10 scale, where 1 represents very soft and 10 represents very firm
- Height reduction of the mattress under a defined vertical load, expressed in millimetres
- Point-by-point firmness distribution across the sleep surface to assess uniformity and left–right symmetry
- Firmness retention, comparing hardness values before and after cyclic durability loading
- Permanent thickness (height) loss following durability cycling, expressed as a percentage
- Component-level indentation force deflection (IFD) values and support factor for foam cores and comfort layers
- Pass/fail sleep-surface firmness assessment for infant mattresses and portable cribs
Adjacent performance items, such as fatigue durability under rolling loads, edge firmness, and structural strength under EN 1725 or equivalent requirements, are frequently bundled with firmness testing to provide a complete performance profile of the product.
Testing Methods
EN 1957 Indentation Firmness Method
The EN 1957 procedure places the complete mattress on a rigid, flat, horizontal support. A circular loading pad, 355 mm in diameter, is pressed vertically onto the surface at specified measurement points. After applying a preload, the force is increased in defined steps up to 400 N, with deflection recorded at each increment once stabilization is achieved. The hardness value H is calculated as the gradient of the force–deflection characteristic between defined points and expressed in N/mm, while the height reduction is determined at maximum load. From these results, the standard derives a firmness rating on a scale from 1 to 10, providing a common European language for comfort grading. Measurements are repeated at multiple defined positions to verify consistency across the sleep surface.
ASTM F1566 Performance Method
ASTM F1566 evaluates the firmness of innerspring, hybrid, and boxspring mattresses and foundations using a circular indenter with a bearing area of 323 cm². Firmness is measured at defined locations across the surface, typically expressed as the force required to achieve a specified compression or the deflection obtained under a specified force. A key strength of this method is its integration with durability assessment: the mattress is first conditioned, then subjected to a cyclic rolling-load fatigue test, after which firmness and height are remeasured. The reported firmness loss and height loss quantify how the product will perform in service. ASTM F1857 establishes the corresponding minimum performance criteria against which these results can be judged.
Component-Level Foam Hardness Testing
For foam cores, memory foam layers, and latex components, hardness is measured at the material level using ASTM D3574 or ISO 2439. Specimens of defined dimensions are placed on a perforated or rigid support, and a standard indenter compresses the sample to specified percentages of its original thickness, typically 25 % and 65 %. The recorded indentation force deflection (IFD) values, together with the calculated support factor, characterize how a foam will feel and how well it will maintain support under increasing body load. These component data are essential for supplier qualification and for predicting finished-mattress firmness during design.
Chinese National and Industry Standards
GB/T 26706 covers palm-fibre elastic mattresses and specifies hardness grading together with durability, hygiene, and emission requirements, while the industry standard QB/T 1952.2 governs spring soft mattresses and defines firmness classification alongside rolling durability and safety provisions. Manufacturers supplying the Chinese market commonly combine these requirements with EN 1957-style firmness characterization to support both domestic compliance and export documentation.
Infant Sleep-Surface Firmness Testing
Because overly soft sleep surfaces are associated with infant suffocation hazards, dedicated methods have been developed for this product category. AS/NZS 8811.1.3 applies a calibrated firmness-testing device to the surface and evaluates it against pass/fail criteria that ensure the surface does not conform excessively around an infant airway profile. Similar sleep-surface firmness provisions are incorporated into crib mattress safety specifications such as ASTM F2933, making firmness testing a mandatory element of infant mattress compliance programs.
Applications
Mattress firmness testing serves stakeholders across the entire product lifecycle. In research and development, instrument-measured hardness data allow engineers to compare spring systems, foam formulations, and layer architectures objectively, shortening design iterations. In manufacturing, periodic firmness verification on production samples confirms process consistency for quilting tension, foam density, and spring assembly.
For brand owners and retailers, standardized firmness ratings support honest labeling of comfort grades and substantiate marketing claims, reducing the risk of misleading advertising and customer returns. Regulatory bodies and market surveillance authorities use firmness and durability data to verify conformity with applicable furniture and infant product requirements, while hotel groups, healthcare facilities, and institutional buyers rely on firmness specifications to procure mattresses that meet defined support criteria. Finally, accredited third-party test reports provide objective technical evidence in supplier disputes, warranty assessments, and import compliance dossiers.
FAQ
What does the EN 1957 firmness rating scale mean?
The EN 1957 firmness rating classifies mattresses on a scale from 1 to 10, where 1 denotes very soft and 10 denotes very firm. The rating is calculated from the measured hardness value and the height reduction under load, giving consumers and buyers a standardized, comparable comfort grade rather than a purely subjective description.
How is the hardness value different from the firmness rating?
The hardness value is a direct physical measurement, expressed in N/mm, describing how much force is needed per millimetre of deflection. The firmness rating converts this measured data, together with height reduction, into a consumer-friendly ordinal scale. Two mattresses with the same rating may therefore show slightly different hardness values depending on their thickness and construction.
How many samples are required and how long does testing take?
Firmness characterization itself is typically performed on one complete production unit per configuration, as testing is non-destructive. When durability-related firmness retention is required, additional dedicated units are needed for the cyclic loading phase. Including conditioning time, a firmness-only evaluation is usually completed within a few working days, while combined durability programs take longer due to the extended fatigue cycling and re-measurement stages.
Does firmness testing cover durability?
Not automatically. Firmness testing measures the initial load-bearing response, but standards such as ASTM F1566 and the Chinese industry standards integrate firmness measurement before and after rolling-load fatigue testing. This produces firmness retention and height loss figures, which describe how the mattress will feel after years of simulated use.
Which firmness level suits which sleeper?
As a general guideline, side sleepers often prefer softer to medium surfaces that cushion the shoulder and hip, back sleepers typically favor medium-firm support for spinal alignment, and stomach sleepers tend to benefit from firmer surfaces that prevent pelvic sinkage. Objective firmness ratings from standardized testing allow retailers to match these preferences with measurable product characteristics rather than vague marketing language.