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Testing flammability of upholstery foam

Foam should be tested for its burning characteristics before being selected for inclusion in furniture.

This article describes how flexible foams used in upholstered furniture are tested for flammability. ‘Flammability’ is a term which is interchangeable with ‘ignitability’, and is one measure of the fire hazard provided by a material.

In the UK, there are strict regulations on the foam used in domestic furniture. Foams must be tested according to the methods set out in the Furniture and Furnishings (Fire)(Safety) Regulations 1988. Only foams which pass the tests can be legally used in upholstery.

What is foam?

A ‘foam’ is a solid or liquid substance formed with bubbles trapped inside it. The type of foam used in furniture is either made from polyurethane or latex rubber (the latter of which may be based on natural materials, but not necessarily so). Polyurethane foam is much more common than latex and is always synthetic. If polyurethane foams are not treated to make them fire-retardant (FR), they represent a considerable fire risk.

A term commonly associated with polyurethane foam is ‘combustion-modified’ (CM). It should be noted that when polyurethane foams burn, they produce lethal gases – including carbon monoxide and hydrogen cyanide. The production of these gases adds to the more obvious hazards associated with fires: in fatal domestic fires, the carbon monoxide is the usual killer.

Types of foam used in furniture

The three main types of foam that we need to consider are:

Foam in block form (figure 1) is in large homogeneous pieces (usually rectangular) usually cut from ‘slab stock’. In crumb form, it is in small, irregularly-shaped scraps, perhaps a few centimetres in length. Crumb foam (figure 2) is sometimes collected from waste after larger blocks have been prepared and is a way of recycling waste.

Figure 1: Polyurethane foam in block form

Sometimes, the crumb foam is bonded to make a reconstituted product, which is similar to foam in block form. This may be multicoloured if the crumb foam pieces are from various foam stocks.

Latex rubber foam (figure 3) is superficially similar in appearance to PU foam. The term ‘latex rubber’ is used to describe a soft rubber which can be partly synthetic, however, it is possible to make 100 per cent natural latex rubber foam.

Figure 2: Polyurethane foam in crumb form

Figure 3: Latex rubber foam blocks

Tests for foams

In the UK, the Furniture and Furnishings (Fire) (Safety) Regulations 1988 specify the tests that must be carried out on foams used in furniture. Unlike the tests specified for upholstery covers, the test used depends on the type of foam. Different foams must always be tested separately, in combination with a non-flammable cover material.

The most common test is the Schedule 1 Part 1 test for polyurethane foam in block form. This test uses a ‘crib 5’ ignition source – a wooden structure about 7cm high representing a significant combustion source (see main photograph). In fire tests, the ignition is generally used to simulate the likely source of heat that the item might encounter, such as a smouldering cigarette. In the case of polyurethane foams, a more severe source is used. This is because the intention of the regulations was to ban all non-CM polyurethane foams, for which the crib 5 test was considered appropriate. Non-CM polyurethane foams were held responsible for several fatal fires in the years before 1988.

The ‘Schedule 1 Part 2’ test is used for polyurethane foam in crumb form. The crumbs are stuffed into the test rig using a standard fabric to contain them in place. An ‘ignition source 2’ (gas flame) is used. The regulations state that as well as the crumb passing this Part 2 test, the foam stock from which the crumb was made must also pass the Part 1 test. This makes it hard to comply with the regulations unless the source of the crumbs is controlled. The ‘Schedule 1 Part 3’ test is used for latex rubber foam. This test also uses ignition source 2.

For details of the tests, reference should be made to the UK regulations and BS 5852: Part 2:1982, while noting a couple of basic aspects. Firstly, the result of these tests is either a pass or a fail – the test does not link to a classification scheme and, therefore, it is not really possible to grade results in terms of fire-retardant characteristics. Secondly, in the tests, an upholstery test assembly is made, which is a combination of a cover material (non-flammable standard polyester fabric) and ­­the foam under test. It is this composite that is tested, not the whole item of furniture.

The importance of testing for flammability

Data published by the UK government’s Home Office indicate a downward trend in deaths and injuries from furniture fires, which can be attributed to the effectiveness of the Furniture and Furnishings (Fire) (Safety) Regulations 1988. Without doubt, polyurethane foams may still pose a fire risk, and it is therefore essential to ensure that furniture products incorporate combustion-modified foam products that will satisfy UK law.

Arranging for SATRA to test your foam

For the schedule 1 part 1 test for polyurethane foam, four pieces of foam, each piece 450 x 450 x 75 mm are required. The permitted tolerance on the dimensions is +/-5 mm on width and length, and +/-2 mm on thickness. When cutting the foam, the use of silicone oil to lubricate saw blades must be avoided, as the resulting contamination may contribute to flammability. If the foam to be tested has already been incorporated into complete items of furniture, SATRA can strip down the item and test the foam, provided there is enough material. If the pieces of foam extracted are too small, then pieces can be put together to fill the test rigs jigsaw-fashion. However, if there are more than two layers of foam, or more than two pieces of foam are used in either plane of the test rig, then the test only has ‘Indicative’ status. This is because there will be a significant deviation from the correct test method – air trapped between layers of foam may increase the likelihood of a fire developing. The test procedure must be carried out twice on duplicate specimens, and both specimens must pass. If there is only sufficient material to fill one test rig, then any pass result will only be indicative.

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