CMHR vs Standard FR Foam Explained

Choosing Between CMHR and Standard FR Foam for UK Upholstery

In the United Kingdom, fire safety regulations governing upholstered furniture are among the strictest in the world. As a specifier, designer, or manufacturer, you must navigate these regulations by choosing the correct grade of fire-retardant polyurethane foam. The two primary categories you will encounter are Standard FR (Fire Retardant) Foam and CMHR (Combustion Modified High Resilient) Foam.

Selecting the wrong foam grade can result in catastrophic fire safety failures, legal liability, and product recalls. This definitive guide by Aerofoam Ltd breaks down the technical differences, testing standards, and use-cases for both foam types.

1. Standard FR Foam (Domestic Grade)

Standard Fire Retardant (FR) foam is the baseline requirement for any foam used in domestic upholstered furniture within the UK. To legally sell a sofa, armchair, or mattress to a domestic consumer in the UK, the foam components must comply with the Furniture and Furnishings (Fire Safety) Regulations 1988.

How it is tested:
Standard FR foam is tested to BS 5852 Part 2. Specifically, it must pass the "Smouldering Cigarette" and "Match Equivalent" tests. During the manufacturing process, standard FR foam is treated with fire-retardant additives (often melamine or halogenated compounds) that delay ignition from small, localized heat sources.

Where it is used:

• Domestic living room furniture (sofas, armchairs)
• Domestic beds, mattresses, and headboards
• Dining chair seat pads in private homes
• Scatter cushions and pillows

2. CMHR Foam (Contract & Commercial Grade)

CMHR stands for Combustion Modified High Resilient foam. This is a highly specialized, heavily treated grade of polyurethane foam engineered for environments where the risk of fire and the potential consequences of a fire are significantly higher than in a domestic home.

How it is tested:
CMHR foam must pass the rigorous BS 5852 Crib 5 test (often referred to simply as "Crib 5" or "Ignition Source 5"). A "Crib" is a small wooden structure made of pine planks glued together in a specific arrangement. It is placed on the foam, soaked in a measured amount of propanol, and set alight. This simulates a much larger, more intense fire (equivalent to four double sheets of broadsheet newspaper burning simultaneously). To pass, the foam must self-extinguish within 10 minutes of the crib being ignited, and the fire must not penetrate through the full thickness of the test rig.

To achieve this remarkable level of fire resistance, CMHR foam is heavily loaded with specialized fire-retardant chemicals (often expanded graphite or high levels of melamine) which causes the foam to char and form a protective crust rather than melting and dripping flaming liquid.

Where it is used:

• Hotels, motels, and guest houses
• Hospitals, care homes, and psychiatric facilities
• Prisons and custodial environments
• Theatres, cinemas, and public waiting areas
• Bars, restaurants, and nightclubs

3. Side-by-Side Comparison: CMHR vs Standard FR

The table below summarizes the critical differences between the two foam grades to help you specify correctly.

4. A Note on Comfort and Durability

A common misconception is that because CMHR foam is heavily treated and dense, it must be uncomfortable or rock-hard. This is false. Advanced manufacturing techniques allow foam converters to produce CMHR foams in incredibly soft, pressure-relieving grades (used in high-end hospital mattresses) as well as firm grades for public transport seating.

Furthermore, because the fire-retardant additives inherently increase the density of the foam, CMHR foams often exhibit superior long-term durability and shape retention compared to their standard FR counterparts.