If you are comparing closed cell foam sheets for an industrial project, a technical data sheet is more useful than a product description alone. It tells you what material was tested, which method was used and what typical figures were obtained. The difficult part is knowing what those figures mean for your particular load, seal, separator or protective insert.
This guide explains the terms that matter most when reading polyethylene foam technical data. We use All Foam AFP30 and AFP45 as examples, but the approach applies when checking specifications from any supplier. The aim is to make purchasing decisions more consistent, not to suggest that one number proves a product will work in every application.
Quick answer
Start with the foam's identity, density and test standard. Compare compression values only where the deflection and testing methods are comparable. Check water absorption, thermal behaviour and dimensional stability when they are relevant. A data sheet reports measured or typical material properties; it is not a guarantee that a finished component will survive a specific load, temperature or service life.
Start with the correct product and revision
Before comparing figures, check the full material name, grade reference, document revision and date. It is easy to quote a number from an obsolete datasheet or from a product with a similar commercial name but a different composition.
All Foam's current technical documents distinguish AFP30 and AFP45 as cross-linked closed-cell polyethylene foams. Ethafoam STPE200 is a separate semi-rigid, non-cross-linked packaging foam with different characteristics and test information.
If a buyer's specification says AFP45, replacing it with AFP30 solely because the products look similar is not a defensible substitution. Where alternatives are allowed, document the equivalence criteria and seek written approval from the relevant designer or customer.
Check the fine print. Typical values are generally not guaranteed minimums, and a technical data sheet does not automatically certify suitability for a finished application.
What density tells you
Density is mass divided by volume, normally expressed in kilograms per cubic metre (kg/m³). It is a way of identifying the amount of material in a given volume, not a direct measure of how a whole finished product will behave.
All Foam lists AFP30 at a nominal 30 kg/m³ and AFP45 at 45 kg/m³. This confirms that AFP45 is the denser of these two grades. It does not mean every 45 kg/m³ polyethylene foam from every manufacturer has identical compression, resilience or other properties.
If density is provided with a standard such as ISO 845, note the testing basis when comparing different products. Ask for the full documentation if a supplier only quotes a marketing grade name without a numerical value or test reference.
Density also differs from thickness. A 10 mm sheet is 10 mm thick regardless of whether its nominal density is 30 or 45 kg/m³. Both dimensions matter for estimating material volume, weight, cut yield and fit.
Compression at 25% deflection
Compression results help indicate the resistance a foam sample offers as it is compressed under specified test conditions. All Foam's AFP30 document lists 62 kPa at 25% deflection under ISO 844, while AFP45 lists 100 kPa at 25% deflection under the same standard.
The figures allow a useful comparison between those named grades at that deflection under the given test method. They indicate that the denser AFP45 sample requires greater compressive stress to reach the stated deformation in the specified test.
They do not establish a maximum safe working pressure for a finished protective pad. A constant load, a sudden drop, cyclic loading and a temperature change are different situations. The final behaviour depends on thickness, pad area, assembly and loading history.
The percentage matters. Comparing one supplier's value at 10% deflection with another supplier's at 25% or 50% is not a direct comparison. Likewise, do not mix standards and call the values equivalent without checking the test conditions.
What the unit kPa actually means
A kilopascal, or kPa, is a unit of pressure or stress. One kPa is 1,000 newtons per square metre. It is not a measurement of total force without knowing the area over which the load is applied.
For illustration, stress and force relate through contact area. A small pad can see a higher stress than a broad pad under the same total load. This explains why converting a technical number into a packaging recommendation requires the actual geometry.
A value measured at 25% sample deflection should not be taken as a permanent service-load limit. It is one point under a particular test, and it does not describe all of the foam's response during dynamic impact or prolonged compression.
If the project needs verified load-bearing behaviour, obtain a design calculation or trial results relevant to the finished assembly.
Compression stress is not compression set
These names sound similar but describe different questions. Compression stress concerns how much force or stress is needed to deform the material to a specified amount during a test. Compression set looks at how much permanent or residual deformation remains after the material has been held compressed under defined conditions and allowed to recover.
A pad can offer high initial resistance while still needing careful evaluation for long-term recovery. For repeatedly used transit inserts or components held compressed in storage, this distinction can matter more than a simple density comparison.
Be careful with test-method references. ISO 1856 covers compression-set testing of specified flexible cellular polymeric materials; it should not be automatically presented as the applicable test for every rigid polyethylene grade. Ask the supplier which method was actually used for the product and whether the data is relevant to your intended loading.
For guidance on why sample and test conditions matter, see the ISO 1856 standard overview and the relevant material-specific test documentation.
Water absorption and the meaning of closed cell
Closed-cell foam has a cellular structure designed to limit water uptake compared with many open-cell materials. That can be important for protective lining, outdoor equipment and applications where moisture exposure is expected.
However, 'closed cell', 'water-resistant', 'waterproof' and 'suitable for permanent immersion' are not interchangeable claims. A data-sheet water-absorption value is normally measured under a stated laboratory method and exposure condition. A finished product may have cut edges, joints, adhesives or other features that influence its practical behaviour.
AFP45's technical data includes a maximum water absorption figure of 1% by volume under its stated internal test. AFP30's document describes the material as non-absorbent and waterproof, and provides separate information concerning cold-water approval.
If water exposure is critical to the design, ask for the full test context and confirm whether the proposed assembly has any separate sealing or regulatory requirements. Do not treat a foam's material property as approval for an entire product.
Working temperature versus test temperature
A technical data sheet may list short-duration dimensional stability at a test temperature. That is not automatically the same as a recommended continuous operating temperature.
The All Foam AFP30 and AFP45 documents include dimensional-stability information for 24 hours at 70°C under an internal method. These figures should be understood as evidence about that specified exposure, not an unconditional approval for continuous use at 70°C or in a hot process environment.
If the foam will be exposed to hot metal, paint curing, cold storage or outdoor extremes, obtain the operating-temperature guidance applicable to the chosen grade. Ask whether the material will be loaded or bonded during exposure because those conditions can change the practical result.
Also consider the other materials in the assembly. A bonding adhesive may have different temperature limits from the foam it is attached to.
Tensile strength and elongation
Tensile strength describes resistance to being pulled apart under a specified test. Elongation describes the extension reached under those conditions, often expressed as a percentage. These properties may matter when thin pieces are stretched during assembly or are at risk of tearing.
Do not assume that a higher density necessarily means greater flexibility. A material can be relatively rigid in sheet form, and geometry often controls how a finished strip bends. If the intended part must wrap around tight corners, ask whether the selected material is suitable rather than relying on density alone.
For sheet spacers that remain flat, compression and dimensional fit may be more relevant than tensile properties. Choose metrics that match the component's function, not simply the longest list of specifications.
What about flame behaviour and approvals?
A foam sheet should never be assumed to meet fire requirements because it is used in construction, insulation or protective packaging. Fire performance is application-specific and must be supported by the required certification for the grade and installation.
All Foam's AFP30 and AFP45 are not sold as fire-retardant grades. If a contract specifies a fire classification, request the exact evidence and test scope rather than interpreting general product descriptions as certification.
The AFP30 data sheet also refers to WRAS approval for cold-water use. That claim belongs to the specified material and scope; it should not be carried over automatically to AFP45 or to every bonded or fabricated assembly made using AFP30.
For higher-risk work, including healthcare, regulated water systems, electrical installations or structural safety components, the relevant designer and compliance specialists should verify suitability.
A comparison example for an industrial buyer
Suppose a drawing requests closed cell foam as a spacer beneath a removable equipment cover. A supplier offers AFP30 and AFP45. It may be tempting to choose the denser grade for 'more protection', but the real decision depends on what the spacer must do.
First, confirm whether the spacer is intended to maintain a gap, support a static load, damp movement or protect the finish. Next, establish the compressed thickness and the acceptable movement under load. Check the contact area and any long-term compression requirement.
The AFP30 and AFP45 compression values can help indicate which samples are worth testing. They cannot alone decide which foam will hold the exact required gap over years of service. If compression set, tolerance, chemical exposure or temperature matters, obtain further evidence and test the finished arrangement.
This process is more reliable than quoting only the nominal density and hoping the spacer behaves as expected. For a finished metal-component example, see closed cell foam for metal protection.
A quick data-sheet reading checklist
Material identity: Full grade name, chemical family, cross-linked or non-cross-linked structure and document revision.
Density: Numerical value, unit and relevant test standard.
Compression: Deflection percentage, test method, units and whether values are typical or guaranteed.
Long-term behaviour: Compression-set or creep information if the component remains under load.
Environment: Water absorption, temperature conditions, chemicals and UV exposure where relevant.
Regulatory evidence: Exact certificates or approvals needed for the real application.
Supply details: Available sheet sizes, thickness, colour, cutting limitations and tolerance requirements.
Test plan: What must be checked on the actual assembled product before sign-off.
Common mistakes when reading technical figures
Comparing different test methods as though they were identical. A number without the method and conditions is easy to misinterpret.
Treating density as firmness. Density is useful but does not uniquely determine a foam's complete mechanical response.
Using compression stress as a safe working-load rating. A single laboratory point does not cover dynamic impacts, fatigue or long-term compression.
Assuming closed cell means zero water uptake. Refer to the actual exposure and measurement conditions.
Assuming material approval equals assembly approval. Other components and installation choices may alter compliance.
Quick answers about closed cell foam data
Quick answer: What does 30 kg/m³ mean?
It is the nominal density of the AFP30 foam grade, expressed as mass per unit volume. It does not mean the finished part can support 30 kg of load.
Quick answer: Is AFP45 firmer than AFP30?
The current All Foam data gives AFP45 a higher compression stress at 25% deflection under the cited method. That supports describing it as the denser, more compression-resistant grade under those conditions, but the overall part geometry still matters.
Quick answer: Are two 25% compression figures always comparable?
Only when the units, standards and relevant test conditions are equivalent. Ask for the method details if they are missing.
Quick answer: Does the data sheet guarantee fitness for my project?
No. Typical properties support informed material selection but do not replace application-specific testing and approval.
Use the data to narrow the choice, then verify it
Technical data sheets are most valuable when they help you decide what to test next. They identify materials with relevant properties, but do not remove the need to consider the finished component and its environment.
Read All Foam's technical data sheets alongside the current AFP30 and AFP45 closed cell foam sheets. If a drawing specifies a particular test standard, tolerance or approval, include that information in a technical enquiry before ordering.
