When comparing foam sheets, density and firmness need to be read as separate properties. Density describes how much foam material is present within a given volume. Firmness describes how strongly the foam resists indentation. A grade can have a higher density without having the firmest feel, and two grades can share a similar firmness while differing in density, recovery and intended use.
Understanding this distinction helps you compare upholstery foam, mattress layers, toppers, packaging grades and reconstituted foam more accurately. It also prevents a common ordering mistake, which is choosing a product from one number or one word instead of considering the complete specification.
The quick answer
Foam density is normally stated in kilograms per cubic metre. It indicates the mass of foam material within a fixed volume. A higher figure means that the same volume of foam contains more material, but it does not tell you exactly how soft or firm the foam will feel.
Foam firmness is a measure of resistance to indentation. In the All Foam technical data sheets for flexible polyurethane grades, nominal hardness is commonly measured at 40 per cent indentation and stated in newtons. A higher newton figure means that more force was required during that test.
Neither figure should be used alone. The correct choice also depends on foam type, recovery, thickness, the surface beneath it and the job the foam needs to perform.
What foam density means
Density is a physical measurement. It compares the weight of the foam with the space it occupies. The All Foam data sheets state density in kilograms per cubic metre and use BS EN ISO 845:1995 as the test standard for the listed flexible foam grades.
For example, the current technical data shows these nominal density ranges:
- Average Soft Foam: 22 to 24 kg/m³.
- Medium Foam: 31 to 34 kg/m³.
- High Firm Foam: 38 to 40 kg/m³.
- Reflex Superior Medium and Reflex Superior Firm: 40 to 42 kg/m³.
- Severe Very Firm Foam: 48 to 52 kg/m³.
- Memory Foam: 48 to 52 kg/m³.
These figures are useful because they show how much material is present in each grade. They do not create a complete comfort rating. Memory Foam and Severe Very Firm Foam share the same stated nominal density range, yet their hardness and recovery are very different.
Density can form part of a durability and application assessment, but it is not a guarantee of service life. The technical data sheets describe their values as typical rather than guaranteed. Use, load, thickness, care, construction and the supporting surface all affect how foam performs in practice.
What foam firmness means
Firmness describes resistance when the foam is compressed. The current flexible foam data sheets list nominal hardness at 40 per cent indentation using BS EN ISO 2439. The result is stated in newtons.
The test gives a consistent way to compare resistance under stated conditions. It should not be read as a promise that every finished cushion, topper or mattress will feel identical. A thin sheet on a hard base can feel very different from a deep cushion made from the same grade. Covers, upper layers and the size of the loaded area also influence the final result.
The listed nominal hardness ranges show clear differences between grades:
- Average Soft Foam: 86 to 110 N.
- Medium Foam: 100 to 130 N.
- Reflex Superior Medium: 100 to 130 N.
- Reflex Superior Firm: 130 to 160 N.
- High Firm Foam: 180 to 220 N.
- Severe Very Firm Foam: 225 to 265 N.
- Memory Foam: 70 to 100 N.
These values demonstrate why density and firmness cannot be treated as the same measurement. The density range may increase while the firmness stays similar, or the density may stay the same while firmness changes substantially.
You can review the current figures in the Foam Data Sheets. For a technical or regulated application, use the relevant data sheet and confirm suitability before ordering.
A clear example using Medium and Reflex Medium foam
The Medium Foam Sheet has a nominal density of 31 to 34 kg/m³ and a nominal hardness of 100 to 130 N. The Reflex Pink Medium Foam Sheet has a higher nominal density of 40 to 42 kg/m³, but its listed nominal hardness is also 100 to 130 N.
This means the two grades can occupy the same stated hardness range even though their density differs. Their product descriptions also distinguish their behaviour. Medium Foam is presented as a versatile grade for general upholstery, back cushions, padding and everyday foam projects. Reflex Medium is described as a premium high resilience grade with instant recovery, suitable for seating and mattresses where responsive recovery is important.
A customer choosing only by the word medium might miss the difference in density and recovery. A customer choosing only by density might assume the Reflex grade must feel much firmer. The complete product information shows that neither assumption is reliable.
A clear example using Reflex Medium and Reflex Firm foam
The Reflex Pink Medium Foam Sheet and Reflex Grey Firm Foam Sheet both have a nominal density range of 40 to 42 kg/m³.
Their firmness differs. Reflex Medium is listed at 100 to 130 N. Reflex Firm is listed at 130 to 160 N.
This is a useful comparison because the density remains the same while the hardness range changes. It shows that a manufacturer can produce grades with a similar amount of material per cubic metre but a different resistance to indentation.
The product descriptions support the same distinction. Reflex Medium is the slightly softer option. Reflex Firm provides a firmer, resilient feel while retaining the quick recovery associated with the Reflex range.
For upholstery, this means you should decide whether the project needs a medium or firmer surface response rather than assuming the denser looking product name will answer the question.
A clear example using Memory Foam and Severe Very Firm Foam
Memory Foam and Severe Very Firm Foam provide the strongest illustration of the difference.
Both data sheets state a nominal density of 48 to 52 kg/m³. Their hardness ranges are very different. Memory Foam is listed at 70 to 100 N, while Severe Very Firm Foam is listed at 225 to 265 N.
Their recovery also differs. Memory Foam is a viscoelastic material that softens with body heat, follows the body and recovers slowly after pressure is removed. Its data sheet lists a recovery rate of 5 to 20 seconds. Severe Very Firm Foam is designed for very firm seating support, particularly where a thinner cushion needs high resistance.
A density figure of 48 to 52 kg/m³ therefore does not describe one particular feel. The foam type, hardness and recovery characteristics completely change how the material behaves.
This is especially relevant when comparing a memory foam mattress topper with firm upholstery foam. Similar density does not make the products interchangeable. Each was developed for a different purpose.
Reconstituted foam needs careful comparison
Reconstituted foam is made from foam fragments bonded together into a dense sheet. The current range includes 6lb and 9lb grades.
The Reconstituted Foam Sheet 6lb has a listed nominal density of 96 kg/m³ with a permitted variation of 10 kg/m³. Its data sheet describes the firmness as very firm.
The Reconstituted Foam Sheet 9lb has a listed nominal density of 144 kg/m³ with a permitted variation of 10 kg/m³. Its data sheet describes the firmness as extremely firm.
These density figures are much higher than the flexible polyether grades discussed above. The data sheets present firmness as an internal rating rather than the same nominal indentation hardness table used for the standard polyurethane grades. This means you should not create a false numerical comparison between measurements that are not presented in the same way.
Use the reconstituted products for the applications stated on their pages. The 6lb grade is intended for firm contract seating and support applications. The 9lb grade is the denser option for industrial matting, gym mats, protective packaging and commercial uses requiring a robust material.
The larger number does not mean the 9lb grade is automatically the better choice for every cushion. It means it is a different, denser product for applications that need that type of construction and resistance.
Thickness changes how firmness is experienced
Firmness data helps compare materials, but finished thickness changes how much foam can compress before the supporting surface beneath it becomes noticeable.
A thin foam sheet placed directly on timber has limited depth available for compression. A deeper cushion made from the same grade has more material between the user and the base. The foam grade has not changed, but the finished experience can change because the construction is different.
This is why a very firm foam may be chosen for a thinner seat cushion, while a deeper cushion can use a different grade. The Severe Very Firm product description specifically notes thinner seating applications where extra firmness is required. Medium Foam is described for deeper domestic seating and general upholstery.
Do not respond to a thickness problem by changing density alone. Measure the available space, check the cover and identify the support below. The Foam Sheet Thickness Guide explains how depth affects upholstery, packaging, closed cell and acoustic applications.
The supporting surface also matters
Foam does not work in isolation. A cushion placed on a solid board receives different support from one placed over webbing or springs. A mattress topper takes its shape from the mattress below it. Packaging foam behaves differently when it is enclosed tightly in a case than when it sits loose inside a large box.
Before selecting a grade, inspect the surface that will carry the foam. A broken seat base, loose webbing or damaged mattress cannot be corrected simply by ordering denser or firmer foam.
For seating, decide whether the base is solid, sprung or flexible. For a topper, confirm that the mattress remains level and supportive. For packaging, identify where the item will contact the foam and whether it can move during handling.
The correct density and firmness only work when the rest of the construction is suitable.
Recovery is another separate property
Recovery describes how the foam returns after compression. It should not be confused with density or firmness.
Reflex Medium and Reflex Firm are both described as instant recovery products. Memory Foam has a deliberately slower response. Standard upholstery grades also recover after compression, but their response should be considered through the complete product specification rather than inferred from density alone.
This matters because two foams can resist pressure in a similar range but feel different as the load moves or is removed. Reflex Medium and standard Medium Foam share a listed hardness range of 100 to 130 N, yet Reflex Medium is selected where responsive recovery and shape retention are important.
When a customer says they want supportive foam, it is therefore useful to ask what support means in that project. They may want a firm initial feel, quick recovery, deeper cushioning or resistance under repeated loading. These are related requirements, but they are not identical.
Density and firmness in upholstery projects
For upholstery, begin with the intended use rather than the colour or grade name.
A headboard or decorative padded panel carries little repeated body weight. The Average Soft Foam Sheet is intended for headboards, light padding, crafts and packaging, but it is not recommended for seating.
A back cushion usually needs a more forgiving feel than a seat base. Medium Foam is a versatile option for back cushions, padding and general upholstery. The correct choice still depends on depth, cover construction and how the furniture is used.
A seat cushion receives concentrated and repeated loading. High Firm Foam is intended for seating and upholstery where extra firmness is required. Reflex Medium and Reflex Firm suit premium seating where recovery and resilience are important. Severe Very Firm Foam is intended for specialist seating that needs very high resistance, particularly at reduced cushion depths.
Reconstituted foam suits dense support and contract applications, but its firm structure may not provide the surface comfort expected from a domestic sofa cushion unless the full construction has been designed for it.
The upholstery foam selection guide explains how to match the grade to seat bases, back cushions, benches, headboards and other furniture projects.
Density and firmness in mattress toppers
A topper changes the upper feel of a mattress, but it relies on the support underneath. The mattress topper range includes products described by material, thickness and comfort feel.
The Memory Foam Mattress Topper uses viscoelastic foam in 2.5cm, 5cm and 7cm depths. It provides a slower, pressure responsive feel rather than the immediate resistance of a firm upholstery grade.
The Medium Density Foam Topper and High Density Foam Topper are both 5cm thick, but one is presented as a medium, softer option and the other as a high, firm option. The Reflex Superior Medium and Reflex Superior Firm toppers provide medium and firm resilient choices with quicker recovery than memory foam.
The words density and firmness in product names help distinguish the options, but the final choice should still consider material, stated feel, thickness and the condition of the mattress. A topper cannot repair sagging or failed support.
Density and firmness in mattresses
A mattress is a complete layered construction, so one foam figure cannot describe the whole product.
The foam mattress range combines an Air Tech ventilation pad, a memory foam comfort layer and a supporting foam base. Deep Sleeper Comfort uses 2 inches of memory foam over 6 inches of Medium Density Foam and is the medium option. Deep Sleeper Back Care uses 3 inches of memory foam over 6 inches of High Density Foam and is the firm option. Luxury Deep Sleeper uses 3 inches of memory foam over 7 inches of Luxury Reflex Foam and is listed as luxury high firm.
The comfort layer and support base perform different jobs. The memory foam upper layer supplies the slower contouring response. The base controls much of the underlying support and stability. Total depth, cover and bed base also contribute to the finished feel.
This is why choosing a mattress only from the density of one layer would be incomplete. Compare the complete layer build and the stated firmness of the finished mattress.
Density and firmness in packaging foam
Packaging applications require a different decision process. The aim may be to hold an item, cushion impact, prevent movement, separate components or create a rigid reusable insert.
A lightweight open cell packaging foam can suit boxes and cases where low weight and cushioning are important. Closed cell polyethylene and Plastazote products provide a firmer, water resistant structure for other applications. Reconstituted foam can suit heavy products where a very dense protective support is required.
The firmest or densest grade is not automatically the safest. Foam that is too hard may provide insufficient cushioning for a delicate item. Foam that is too soft may compress until the product contacts the case. The correct solution depends on the item weight, shape, fragility, clearance and handling conditions.
Use the Packaging Foam Sheets Guide to compare the current flat packaging foam, anti static foam, semi rigid and closed cell grades, and dense reusable inserts. The separate flat versus convoluted guide remains available for customers researching older profiled case linings.
How to read a foam data sheet
A data sheet provides more useful information than one marketing label. Read it in a clear order.
First, confirm the product and grade reference. Similar product names should not be assumed to share the same specification.
Second, read the product description and typical applications. These sections explain what the grade was developed to do and where it should not be used.
Third, check density and hardness separately. Record the units and test methods. Do not compare kilograms per cubic metre with newtons as though they measure the same property.
Fourth, review recovery, tensile strength, elongation, compression set and any other listed properties when they are relevant to the project. Not every data sheet presents the same tests, so compare only like with like.
Fifth, read the fire performance statement and limitations. Fire information must match the intended application and finished product requirements. A general product statement should not be expanded into a claim that is not written in the source document.
Finally, remember that listed values are normally typical. They are not a guarantee of service life or suitability for every project. For healthcare, contract, regulatory or other critical uses, confirm the specification before ordering.
Common mistakes when comparing density and firmness
The first mistake is assuming that high density always means hard. Memory Foam and Severe Very Firm Foam show why this is incorrect. Their stated density ranges match, but their hardness and recovery are very different.
The second mistake is assuming that two products with the same firmness are identical. Medium Foam and Reflex Medium share the same listed hardness range, but Reflex Medium has a higher density and a different recovery profile.
The third mistake is choosing by colour. Foam colour helps identify some grades, but it is not a universal performance scale. Use the product name and specification.
The fourth mistake is ignoring thickness. A suitable grade at the wrong depth may not perform as expected.
The fifth mistake is treating every application as seating. Headboards, cot mattresses, sofa cushions, packaging inserts, acoustic panels and mattress layers require different properties.
The sixth mistake is using a technical figure as a guarantee. Density and hardness help comparison, but the finished result also depends on construction, load, use and care.
A practical selection process
Use this sequence before ordering.
- Define the application. State whether the foam is for a seat, back cushion, headboard, mattress layer, topper, packaging insert or another use.
- Measure the required size. Check the length, width and thickness of the cover or surrounding space rather than guessing.
- Decide what firmness is needed. Consider whether the foam should feel soft, medium, firm or very firm in the finished construction.
- Check density and product type. Use these details to distinguish grades that may share a similar firmness.
- Review recovery and construction. Decide whether quick resilience, slow memory response or dense bonded support is required.
- Check the supporting surface. Repair weak bases, broken slats or damaged structures before fitting new foam.
- Read the application guidance. Confirm fire and technical requirements where they matter.
- Compare the complete specification. Do not choose from one number alone.
This process turns density and firmness into useful information rather than competing labels.
The final difference
Density tells you how much foam material is contained within a given volume. Firmness tells you how strongly the material resists indentation under a stated test. They describe different parts of foam performance.
The All Foam range gives several clear examples. Reflex Medium and Reflex Firm share the same density but differ in hardness. Medium Foam and Reflex Medium share the same hardness range but differ in density and recovery. Memory Foam and Severe Very Firm Foam share the same stated density range but have completely different hardness and response.
Choose the foam by matching density, firmness, recovery, thickness and intended use. When those details are considered together, product names and technical figures become much easier to understand.
