Choosing between open cell foam and closed cell foam sheets starts with the job the material must perform. Open cell foam is generally selected when compression, cushioning or acoustic absorption matters. Closed cell foam is generally selected when the project needs a more sealed structure, lower water absorption, firmer protection, lining or sealing.
Browse the dedicated closed cell foam sheets page when the project needs AFP polyethylene or EPDM options with live sizes, thicknesses and prices. Ethafoam STPE200 remains in the separate Packaging Foam Sheets range as a semi-rigid packaging material.
That quick distinction is useful, but it is not enough to choose a product. Open cell and closed cell describe cell structure rather than one fixed level of firmness, density or durability. Two products from the same group can still behave very differently. The material family, thickness, density, compression response, backing and intended application all need to be considered together.
The Plastazote foam sheets guide and EPDM foam sheets guide explain two specialist closed-cell options in more detail.
The quick answer
Open cell foam contains connected cells that allow air to move through the structure. This construction is common in flexible cushioning, upholstery, mattresses, packaging foam and acoustic treatment. It can compress readily and is available in a wide range of comfort and firmness grades.
Closed cell foam contains cells that are separated more completely from one another. The structure usually absorbs less water and often feels firmer or more rigid than flexible open cell polyurethane foam. It is commonly used for protective inserts, lining, seals, gaskets, gap filling and applications where a more stable sheet is required.
Neither type is automatically better. Open cell foam can be the correct choice for a sofa cushion but the wrong choice for a weather seal. Closed cell foam can be the correct choice for a case insert but the wrong choice for a soft back cushion. The dedicated packaging foam sheets page groups flexible, semi rigid, anti static, closed cell and dense protective foam by intended use.
What cell structure actually means
Foam is made from a network of cells. The way those cells are formed affects how air, water and pressure move through the material.
In open cell foam, many cell walls are open or connected. Air can move as the foam is compressed and released. This helps create the familiar feel of flexible upholstery and comfort foam. It also allows acoustic foam to receive sound energy within its structure rather than presenting a solid surface.
In closed cell foam, the cells are more fully enclosed. Air and gas are held within separate pockets, and liquid has fewer direct routes through the material. This produces the lower water absorption and more stable structure associated with many polyethylene and rubber foam sheets.
Cell structure does not tell you every property. A closed cell rubber foam can be flexible, while a closed cell polyethylene sheet can be comparatively rigid. An open cell memory foam can recover slowly, while an open cell Reflex foam can recover quickly. Always read the complete product description rather than choosing from the words open cell or closed cell alone.
How open cell foam behaves
Open cell foam is usually selected because it can compress, cushion and recover. The open structure allows air to move when load is applied. The exact feel depends on the foam grade, density, hardness and thickness.
A softer grade can suit headboards, padding and light comfort applications. Medium and firm upholstery grades can support seating. Memory foam responds slowly and follows body shape. Reflex foam is designed for quicker recovery. Packaging foam can absorb impact without adding excessive weight. Acoustic foam uses its open structure to help reduce reflections within a room or enclosure.
This range of behaviour explains why the phrase open cell foam is not a complete product specification. A memory foam topper, a firm seat cushion and an acoustic panel may all use open cell structures, yet they are not interchangeable.
The current All Foam technical sheet for charcoal acoustic foam identifies it as open cell acoustic polyurethane foam. It lists a nominal density of 24 to 27 kg per cubic metre and a nominal hardness of 115 to 150 N. The packaging foam data sheet identifies a flexible polyurethane grade with a nominal density of 18 to 22 kg per cubic metre. Those figures show that even within open cell applications, products are designed around different functions.
How closed cell foam behaves
Closed cell products generally provide a more sealed and stable structure. They can offer low water absorption, dimensional stability and useful resistance under load. The final behaviour depends strongly on whether the material is polyethylene, Plastazote or EPDM rubber.
AFP30 and AFP45 are cross linked polyethylene sheets. AFP45 has a higher density and higher compression resistance than AFP30. Plastazote LD33 is a nitrogen expanded cross linked polyethylene foam with a fine cell structure and a broad colour range. EPDM is a flexible synthetic rubber foam intended for sealing, cushioning and protective applications. Ethafoam STPE200 is treated separately by All Foam as a semi rigid packaging material for cushioning and gap filling.
These materials all belong within the closed cell group, but they answer different requirements. The correct selection depends on load, flexibility, environment, appearance, fabrication and the shape of the finished part.
Open cell foam for upholstery and comfort
The upholstery foam sheets section includes grades for headboards, cushions, seats, mattress layers and general padding. These products are chosen according to the required feel and support rather than moisture resistance.
Average Soft Foam is intended for headboards, light padding, crafts and packaging, but it is not recommended for seating. Medium Foam is a versatile option for back cushions, deeper domestic seating and general upholstery. High Firm Foam suits seating that needs greater resistance. Reflex Medium and Reflex Firm provide more responsive recovery. Severe Very Firm Foam is intended for specialist firm seating, particularly where available cushion depth is limited.
The key decision is not simply open cell versus closed cell. It is the combination of grade, firmness, thickness, recovery and the support beneath the foam. A closed cell polyethylene sheet may resist moisture well, but it does not provide the same type of comfort as a flexible upholstery foam.
The upholstery foam guide explains how seat bases, back cushions, benches and headboards place different demands on the material.
Open cell foam for mattresses and toppers
Mattress and topper foams use different responses to create different surface feels.
Memory foam softens with body heat and recovers slowly after pressure is removed. Reflex foam has a quicker response. Standard medium and high density foams provide more immediate support. These differences come from the complete foam formulation and construction, not from cell structure alone.
The current All Foam mattresses combine a memory foam comfort layer with a supporting foam base. Deep Sleeper Comfort uses Medium Density Foam beneath the memory foam. Deep Sleeper Back Care uses High Density Foam. Luxury Deep Sleeper uses Luxury Reflex Foam. The layers work together, so choosing a mattress requires comparison of the full construction rather than one material label.
A topper also relies on the mattress below it. Open cell comfort foam can change the upper feel of a sound mattress, but it cannot repair broken support, deep sagging or a failed bed base.
Open cell foam for acoustic treatment
Open cell acoustic foam is designed to help reduce reflections and reverberation within a room, enclosure or recording space. Sound energy enters the cellular structure and is reduced as it moves through the material.
The acoustic foam sheets section currently includes flat standard fire retardant and flat Class 0 options. Thickness, area covered, position and room construction all affect the finished result.
Acoustic foam is used for treatment inside a space. It should not be confused with sound isolation. Preventing sound from passing through walls, ceilings, floors, doors or gaps usually requires a complete construction involving mass, sealing and structural separation. Adding open cell foam to a wall does not turn that wall into a soundproof barrier.
The flat and convoluted acoustic foam guide explains the difference between the two surface formats and clearly identifies the flat products currently supplied by All Foam.
Open cell foam for protective packaging
Flexible open cell packaging foam is useful when a product needs cushioning, impact attenuation and low weight. It can be cut to line boxes, cases and equipment containers.
The Packaging Foam Flat Sheet is available in several sheet sizes and thicknesses from 6.3mm to 101.6mm. The Antistatic Pink Packaging Sheet AS22 is intended for electronics and other sensitive items. Convoluted packaging foam is not currently listed as a purchasable All Foam sheet.
Open cell packaging foam can be the right choice where the material must compress around an item and absorb movement. It may not be the right choice where the insert needs a more rigid shape, very low water absorption or a clean cut presentation across repeated handling cycles.
The packaging foam selection guide covers movement, clearance, item weight, electronics and reusable cases in more detail.
Closed cell polyethylene for lining and protection
The Closed Cell Polyethylene Sheet AFP30 is a rigid black or white sheet with a non absorbent, waterproof structure. The technical data sheet lists a density of 30 kg per cubic metre and compression at 25 per cent deflection of 62 kPa. It is available in thicknesses from 2mm to 100mm.
AFP30 suits lining, protective packing, sealing and general practical applications that need a closed cell polyethylene sheet. Its two colour options also allow the material to be matched more closely to the finished project.
The Closed Cell Polyethylene Sheet AFP45 has a higher listed density of 45 kg per cubic metre and compression at 25 per cent deflection of 100 kPa. It is more rigid than AFP30 and is intended for more demanding packing, lining and sealing applications.
The comparison between AFP30 and AFP45 shows why cell structure alone is not enough. Both are closed cell polyethylene products. The difference in density and compression response changes the level of support and rigidity they provide.
Use AFP30 where a rigid closed cell sheet is needed but the higher resistance of AFP45 is unnecessary. Consider AFP45 where heavier items or greater loading require a firmer insert. Final suitability still depends on thickness, contact area, item weight and the full construction.
Plastazote LD33 for finish and fabrication
Plastazote LD33 is a nitrogen expanded cross linked polyethylene foam. Its technical data sheet lists a density of 33 kg per cubic metre, compression at 25 per cent deflection of 69 kPa and negligible water absorption.
The product is available in a wide range of colours and is supplied unbacked. It can also be fabricated and thermoformed into more complex shapes.
Plastazote can suit protective inserts, displays, props, models and projects where appearance, finish and workability matter. A coloured Plastazote sheet may provide a more deliberate presentation than a basic black packaging insert.
This does not mean Plastazote is the correct choice for every closed cell project. A simple lining job may not need its colour range or fabrication qualities. A heavier loading requirement may point towards a different grade. Choose it when its combination of fine cell structure, colour, workability and low water absorption answers the project brief.
Ethafoam as a separate semi rigid packaging option
Ethafoam STPE200 Semi-Rigid Packaging Foam Sheet is kept in All Foam’s packaging range rather than the closed cell range. It is available in white or grey, in sheet sizes of 100cm by 120cm and 200cm by 120cm, with thicknesses from 5mm to 100mm.
STPE200 is a semi-rigid, non-cross-linked expanded polyethylene packaging foam for cushioning, gap filling and impact absorption. It also has low water absorption and good dimensional stability across its stated working temperature range.
Ethafoam can suit transit protection, structural gaps, protective barriers and industrial cushioning. Its response differs from flexible open cell packaging foam. It provides a more stable shape while retaining cushioning properties suited to medium and heavy items.
The product is not fire retardant. Where fire performance matters, the requirement must be identified before ordering and an appropriate alternative confirmed.
EPDM for flexible seals and weather exposure
EPDM Closed Cell Rubber Sheet is a flexible synthetic rubber foam rather than a polyethylene sheet. It is used for sealing, cushioning, anti rattle padding and protective applications.
The technical data lists resistance to UV exposure, ozone and weathering. It is available in 2.5mm to 20mm thicknesses.
EPDM is useful where the material must remain flexible around a joint, door, panel or uneven contact surface. A rigid polyethylene foam may not follow the same movement or compression pattern.
Cell structure again provides only the starting point. EPDM and AFP45 are both closed cell materials, but one is a flexible rubber foam and the other is a rigid polyethylene foam. Their applications overlap in some areas, yet their handling and finished response are different.
Moisture resistance and waterproof claims
Closed cell foam is normally chosen over open cell foam when lower water absorption matters. This is one of the clearest practical differences between the two groups.
However, do not turn that general rule into a claim that every closed cell product is identical or suitable for permanent immersion. AFP30 and AFP45 are described as waterproof and non absorbent. Plastazote is described as having negligible water absorption. EPDM is selected for weather resistant sealing applications. Ethafoam has separate packaging guidance and should not be grouped into the All Foam closed cell range.
These descriptions are not interchangeable. The correct product depends on the exposure, pressure, temperature, chemicals, joint design and length of contact. A technical or regulated application may require specific testing or approval beyond the general product description.
Open cell foam can receive and hold moisture more readily because air and liquid can move through the connected structure. It should not be chosen as a water barrier. If open cell foam becomes wet, the drying conditions and hygiene requirements of the finished use also need consideration.
Firmness and density do not follow one simple rule
Closed cell foam often feels firmer than comfort foam, but the words open cell and closed cell do not create a universal firmness scale.
AFP45 is more rigid than AFP30 because it has a higher density and compression resistance. EPDM remains flexible despite its closed cell structure. Open cell High Firm Foam is designed for firm seating, while open cell Memory Foam is designed for a slower contouring response.
This is why density, hardness, compression resistance and recovery must be read separately. The foam density and firmness guide explains how products can share a similar density while feeling very different, or share a similar hardness range while differing in recovery and construction.
When comparing open cell with closed cell foam, begin with the required function. Then use density and compression information to compare products within the suitable material group.
Thickness affects the finished result
A correct material at the wrong thickness can still perform poorly.
Thin closed cell sheets can work as liners, seals, separators and surface protection. Deeper sheets can create shaped inserts, impact zones or gap filling sections. A 2mm EFP sheet and a 100mm EFP sheet are the same product family, but they answer very different physical requirements.
Open cell foam thickness changes the available compression depth. A thin upholstery sheet over timber will feel different from a deep seat cushion. A thin acoustic sheet and a deep acoustic panel do not present the same amount of material to sound energy. A packaging insert must provide enough clearance to cushion the product without allowing it to strike the case.
Measure the finished space, not only the old foam. Check covers, lids, hinges, fittings, item movement and the support below. The foam sheet thickness guide explains how to match depth to upholstery, packaging, closed cell and acoustic applications.
Plan the fixing method separately
The current All Foam AFP30, AFP45, EPDM and flat acoustic sheets are supplied unbacked. This lets the retention or bonding method be selected separately around the substrate and finished application.
Where a bonding system is used, surface preparation and compatibility still matter. Dust, oil, loose paint, texture and repeated movement can affect the finished installation.
Fire performance must be checked separately
Open cell and closed cell are structural descriptions. They do not tell you whether a product is fire retardant.
The standard flat packaging foam is described as not fire retardant and not suitable for upholstery. Ethafoam, which sits separately in the packaging range, is also described as not fire retardant. AS22 packaging foam is fire retardant. The acoustic range includes fire retardant and Class 0 products. The current EPDM technical data sheet focuses on its closed cell structure and resistance to UV, ozone and weathering rather than stating a fire classification, so a fire requirement must be confirmed separately.
Do not assume that all polyurethane foam has the same fire performance. Do not assume that a closed cell product is safer because it absorbs less water. Check the exact product page and technical data sheet for the intended application.
For furniture, contract, public space, transport, construction or other controlled uses, confirm the relevant requirement before ordering. The fire retardant foam guide explains why product wording, test information and the finished assembly all matter.
How to choose between open cell and closed cell foam
Use a structured process rather than starting with colour or price.
1. Define the purpose. Decide whether the foam must provide comfort, absorb impact, reduce reflections, line a case, create a seal, fill a gap or resist moisture.
2. Identify the required behaviour. Consider softness, rigidity, recovery, flexibility, water exposure, appearance and repeated loading.
3. Choose the material group. Open cell polyurethane is usually the starting point for comfort, flexible cushioning and acoustic absorption. Closed cell polyethylene, Plastazote or EPDM is usually the starting point for lining, sealing, low water absorption and more stable protection.
4. Select the grade. Compare the products within that group. AFP30 and AFP45 are not the same. Plastazote and Ethafoam are different material types; Plastazote is no longer part of the current All Foam product range. Medium Foam and Reflex Medium are not the same.
5. Measure the available space. Record length, width and depth. Allow for covers, lids, compression, movement and any adhesive layer.
6. Check fire and environmental requirements. Confirm whether the product needs a particular fire statement, colour, backing, approval, temperature range or exposure resistance.
7. Review the technical information. Use the Foam Data Sheets for current properties and contact the technical team where the application is regulated or critical.
Common mistakes to avoid
The first mistake is choosing closed cell foam whenever a project might encounter occasional moisture. The real question is how much exposure exists and what else the foam must do. A soft cushion and a weather seal require different materials even when both may encounter moisture.
The second mistake is choosing open cell foam for every cushioning task. A reusable equipment case may need the shape stability of a closed cell insert. A delicate item may need a combination of firmer support and softer contact layers.
The third mistake is assuming that closed cell always means hard. EPDM is flexible, while AFP45 is more rigid than AFP30. Ethafoam is a separate semi rigid packaging option rather than part of the All Foam closed cell range. The material family and grade matter.
The fourth mistake is using colour as a specification. Black, white, grey or coloured sheets can help identification and appearance, but colour alone does not confirm density, fire status or material type.
The fifth mistake is ignoring thickness. A suitable foam grade cannot protect an item if the design gives it too little space to compress or distribute load.
The sixth mistake is treating acoustic foam as soundproofing. Open cell acoustic foam can improve internal sound treatment, but it does not replace a complete isolation construction.
The seventh mistake is assuming fire performance from cell structure. Always check the named product and the intended use.
Which foam is right for common projects?
For a sofa seat or back cushion, begin with open cell upholstery foam and choose the grade from the required support, recovery and depth.
For a mattress comfort layer or topper, use the appropriate memory, medium, high density or Reflex foam rather than a closed cell packing sheet.
For room reflections and reverberation, use an open cell acoustic product with the required profile, thickness and fire performance.
For a lightweight protective box insert, flexible open cell packaging foam may provide the required cushioning with lower weight.
For a reusable case that needs a cleaner, firmer closed cell insert, consider AFP30 or AFP45 according to load and required rigidity. If the requirement is semi-rigid packaging cushioning instead, compare Ethafoam separately.
For lining, separators and low water absorption, a closed cell polyethylene sheet is usually more appropriate than flexible upholstery foam.
For a gasket, door seal or weather exposed joint, EPDM may be more suitable because it combines a closed cell structure with flexibility and weather resistance.
For a project where fire performance is important, choose from products with the required documented status rather than selecting from cell structure alone.
Final guidance
Open cell foam is the usual choice for comfort, flexible cushioning, acoustic absorption and many packaging applications. Closed cell foam is the usual choice for lower water absorption, firm inserts, lining, sealing and protective applications that need a more stable structure.
The best result comes from treating cell structure as the first filter rather than the final answer. Once the correct group is identified, compare the material family, grade, thickness, compression response, backing, fire information and finished environment.
Browse the complete Foam Sheets range to compare upholstery, packaging, closed cell and acoustic products in one place. For a technical, regulated or unusual project, review the relevant data sheet and confirm suitability before ordering.
