Which Fabrics and Fibres Can Be FR Treated: A Guide for Interior Designers

Fibres that can generally be treated: Cotton, linen, wool, mohair, silk, viscose, polyester (with conditions), nylon, modacrylic
Fibres to avoid for FR treatment: Acrylic, polypropylene, polyethylene, pure acetate or triacetate
Exempt fibres (domestic upholstery): Cotton, linen, wool, silk, viscose — do not require match test treatment if at least 75% natural fibre by weight with a Schedule 3 interliner
The single most important rule: Fibre type is a guide, not a guarantee. The specific fabric construction, dye type, and finish all affect treatability. Always confirm with the treatment provider before ordering.

A fabric that cannot be successfully FR treated is a fabric that cannot be legally used in a contract environment without an alternative compliance route. Discovering this after the fabric has been specified, ordered, and delivered is a significant problem. This guide explains which fibres and fabric types are treatable for the UK standards most commonly required in contract interiors, which should be avoided, and what the exemption rules mean for domestic upholstery.

For the fire standards that require treatment, see our Crib 5 guide and our hotel fabric specification guide. For how dye type affects FR treatment, see our dye types and FR treatment compatibility guide.

How Treatability Works

FR treatment works by introducing a chemical compound — typically phosphorus-based or halogenated — into or onto the fabric structure. For the treatment to be effective, the compound must be able to penetrate and adhere to the fabric in sufficient quantity to inhibit combustion. The fibre type determines whether this is chemically and physically possible.

Natural protein fibres — wool, mohair, silk — have an inherently higher resistance to ignition than cellulosic and synthetic fibres, which reduces the amount of chemical treatment required to achieve compliance. This is one reason protein fibre fabrics can often be treated successfully even at relatively low chemical loadings.

Cellulosic fibres — cotton, linen, viscose — ignite readily and require more chemical treatment to achieve compliance. They can generally be treated successfully, but the dye type carried on the fabric affects whether the treatment can be applied without causing colour change. See the dye types and FR treatment guide for detail on this.

Synthetic fibres present a different challenge. Some — polyester, nylon — can be treated. Others — acrylic, polypropylene, polyethylene — melt and flow when exposed to heat rather than forming a char, which FR chemicals cannot effectively prevent. Fabrics containing significant proportions of these fibres cannot be reliably FR treated.

Fibre by Fibre: Treatability for UK Contract Standards

Cotton. Can be treated for both Crib 5 upholstery and BS 5867 Part 2 Type B curtains. Cotton is one of the most commonly treated fibres in the UK contract market. Back-coating is the standard method for upholstery Crib 5. Wet padding is used for curtain treatment. Dye type matters: reactive-dyed cotton carries a risk of post-treatment colour change and should be confirmed with the treatment provider before committing to an order. In domestic upholstery, cotton is an exempt fibre — fabric of at least 75% cotton by weight does not require match test treatment if used with a Schedule 3 fire-retardant interliner.

Linen. Can be treated for Crib 5 and BS 5867. Linen is an exempt fibre for domestic upholstery at 75% or above by weight with a Schedule 3 interliner. For contract use, treatment is required and linen takes FR chemical treatment well when correctly applied. The same reactive dye caution applies as for cotton.

Wool. Can be treated. Wool is a protein fibre with natural fire resistance arising from its high nitrogen and sulphur content. It is an exempt fibre for domestic upholstery. For contract upholstery requiring Crib 5, wool can be back-coated. The treatment chemical loading required is typically lower than for cotton because of wool’s inherent resistance. Wool treated with FR chemicals retains its handle well compared to some other fibres. An exempt fibre for domestic use.

Mohair. Can be treated, and Kothea’s active ranges carry independently certified Crib 5 passes achieved without topical treatment on the tested ranges, meaning treatment is not required. Where a mohair velvet does not carry an inherent certification, it can be back-coated. Mohair is not listed as an exempt fibre for domestic upholstery under the Furniture and Furnishings (Fire) (Safety) Regulations, which means it does not qualify for the Schedule 3 interliner route at any fibre content level. It requires treatment for domestic match test compliance unless it passes the test inherently.

Silk. Can be treated with care. Silk is an exempt fibre for domestic upholstery. For contract use, silk can be back-coated for Crib 5 but the treatment process must be managed carefully — silk is a delicate fibre and incorrect application can alter handle and appearance. Silk velvet in particular is sensitive to any wet process and should be approached with specialist advice before treatment is specified. The low Martindale rub count of silk velvet means it is unlikely to be specified for most contract upholstery applications regardless of fire treatment status.

Viscose and modal. Can be treated. Viscose (also called rayon) is a regenerated cellulose fibre and behaves similarly to cotton in FR treatment. It is an exempt fibre for domestic upholstery. For contract use it can be back-coated or wet-padded. Viscose is prone to shrinkage in wet processes and the treatment must be applied with appropriate tension control. Modal (polynosic) is a modified viscose and is also generally treatable.

Cuprammonium (cupro). Can be treated but is not an exempt fibre. Less commonly encountered in upholstery specification but treatable by similar methods to other regenerated cellulosics.

Acetate and triacetate. Problematic. Acetate and triacetate are cellulose acetate fibres with thermoplastic properties — they melt and drip when heated. This makes effective FR treatment very difficult. Treatment is only practically viable when acetate or triacetate are present as minor components in a blend with natural fibres. Fabrics with significant acetate or triacetate content should be avoided for contract applications requiring FR treatment. Not exempt fibres for domestic use.

Polyester. Can be treated when blended with natural fibres. Pure polyester is a thermoplastic fibre — it melts rather than chars — and standard FR back-coating compounds are less effective on pure polyester than on natural fibres. However, polyester blended with natural fibres at significant proportions can be treated. Trevira CS is a permanently flame-retardant polyester fibre whose fire resistance is inherent to the polymer and does not require topical treatment. Standard polyester in blend with cotton or wool at 50% or above natural fibre content is typically treatable by back-coating. Confirm the specific blend and proposed treatment method with the treatment provider.

Nylon (polyamide). Can be treated when blended with natural fibres. Similar position to polyester — thermoplastic in its pure form, more treatable in natural fibre blends. Nylon 6,6 blended with wool or cotton at significant proportions can generally be back-coated for Crib 5.

Modacrylic. Can be treated. Modacrylic is a modified acrylic fibre with significantly better inherent fire resistance than standard acrylic. It is treatable for both upholstery and curtain standards and behaves well in FR treatment processes.

Acrylic. Avoid. Standard acrylic (at least 85% acrylonitrile) is thermoplastic and melts and drips when exposed to heat. FR chemicals cannot effectively prevent this behaviour. Acrylic should not be specified for contract applications requiring FR treatment. This applies to both upholstery and curtain use. Not an exempt fibre.

Polypropylene. Avoid. Polypropylene burns readily and melts at low temperatures. It cannot be reliably FR treated to UK contract standards. Not an exempt fibre.

Polyethylene. Avoid. Same position as polypropylene — melts and burns without forming a char. Not treatable. Not an exempt fibre.

The Domestic Exemption: What It Means in Practice

The Furniture and Furnishings (Fire) (Safety) Regulations define a category of exempt fibres for domestic upholstery. A fabric composed of at least 75% by weight of exempt fibres — alone or in combination — does not require treatment for the match test (BS 5852 Source 1), provided it is used with a fire-retardant Schedule 3 interliner. It must still pass the cigarette test (BS 5852 Source 0).

The exempt fibres are: cotton, linen (flax), wool, silk, viscose (rayon), modal (polynosic). Mohair is not on the exempt list despite being a natural protein fibre with good inherent fire resistance. A fabric of 100% mohair does not qualify for the Schedule 3 interliner route and must pass the match test by another means — either inherently or through topical treatment.

The exemption applies to domestic upholstery only. It does not apply to contract upholstery, where Crib 5 or BS 7176 certification is required regardless of fibre content. A fabric of 100% cotton used on a domestic sofa with a Schedule 3 interliner is compliant for domestic sale. The same fabric on a hotel chair requires Crib 5 certification.

The Schedule 3 interliner must itself be fire retardant to the required standard. It cannot be a standard curtain interlining or a general-purpose backing fabric. The interliner supplier should provide confirmation that the product meets the Schedule 3 requirement.

Fabric Construction and Finishes That Affect Treatability

Fibre type is the primary determinant of treatability but not the only one. The following fabric characteristics can affect whether a treatment will be effective or practical.

Pile fabrics. Velvet and other pile fabrics present additional considerations for FR treatment. The pile surface increases the volume of combustible material at the surface relative to a flat-woven fabric of the same fibre and weight. A pile fabric may require a higher chemical loading to achieve compliance than a flat-woven fabric of the same fibre. The pile structure also means that any visible effect of treatment — colour change, handle alteration — is more noticeable than on a plain fabric. Treatment must be applied from the back only, without penetrating the pile face.

Coated or laminated fabrics. Fabrics with a polymer coating or laminate backing may not be treatable by standard back-coating methods because the existing coating prevents adhesion of the FR compound. Faux leather and coated technical fabrics typically achieve their fire performance through the inherent properties of the coating compound rather than topical FR treatment.

Water-repellent or stain-resistant finishes. Some fabrics carry a Teflon, Scotchgard, or similar fluorocarbon finish for stain resistance. These finishes can reduce the penetration of FR chemicals into the fabric structure, potentially reducing treatment effectiveness. Confirm with the treatment provider whether the specific finish is compatible with the proposed treatment method before ordering.

Very lightweight fabrics. Sheer curtain fabrics and extremely lightweight upholstery fabrics may be difficult to treat without visible handle change or shrinkage, regardless of fibre type. The chemical loading required for compliance may be a higher proportion of the fabric weight than for a heavier cloth, making the treated fabric noticeably different in handle from the untreated original.

What to Ask Before Specifying a Fabric for FR Treatment

Before specifying a fabric that will require topical FR treatment for contract use, confirm the following with the fabric supplier and with the proposed treatment provider.

What is the full fibre composition by percentage? The fibre content label gives this, but confirm with the supplier whether any blend components are thermoplastic — polyester, nylon, acrylic — and at what proportion.

Does the fabric carry any surface finish — stain resistance, water repellency, or coating — that might affect FR treatment penetration?

What is the dye class? See the dye types and FR treatment guide for why this matters.

Has this specific fabric been successfully FR treated before, and to which standard? Treatment providers keep records and can often advise whether a specific fabric has been through their process previously.

Is the treatment provider UKAS-accredited to issue the certificate required for the project? For contract upholstery the certificate must be issued by a UKAS-accredited laboratory. No fabric company or designer can self-certify FR compliance.

Frequently Asked Questions

Can all fabrics be made fire retardant?

No. Fibres that melt rather than char when heated — acrylic, polypropylene, polyethylene, and pure acetate — cannot be reliably FR treated to UK contract standards. FR chemicals work by inhibiting combustion in fibres that burn; they cannot prevent the melt-and-drip behaviour of thermoplastic fibres. Fabrics containing significant proportions of these fibres should not be specified for contract applications requiring Crib 5 or BS 5867 compliance through topical treatment.

Can polyester be FR treated?

Pure polyester is thermoplastic and difficult to treat effectively by standard back-coating methods. Polyester blended with natural fibres at substantial proportions — typically 50% or more natural fibre — can generally be back-coated for Crib 5. Trevira CS is a permanently flame-retardant polyester fibre with inherent fire resistance that does not require topical treatment. Always confirm the specific blend composition and proposed treatment method with the treatment provider before specifying.

Does a fabric with 75% natural fibre content need FR treatment for contract use?

Yes. The 75% natural fibre exemption applies only to domestic upholstery under the Furniture and Furnishings (Fire) (Safety) Regulations, allowing the use of a Schedule 3 interliner in place of match test treatment. It does not apply to contract upholstery, where Crib 5 or BS 7176 certification is required regardless of fibre content. A hotel, restaurant, or other commercial environment requires certified FR compliance irrespective of whether the fabric is made from exempt fibres.

Can mohair velvet be FR treated?

Mohair velvet that does not carry an inherent Crib 5 certification can be back-coated for Crib 5. However, Kothea’s active mohair velvet ranges carry independently certified Crib 5 passes on the tested ranges without topical treatment, which removes the need for treatment entirely. Mohair is not an exempt fibre under the domestic regulations regardless of fibre content, so it requires Crib 5 compliance by inherent certification or topical treatment for all contract applications.

Will FR treatment change how my fabric looks or feels?

Back-coating applied correctly to upholstery fabric does not typically alter the appearance or handle of the face. Wet-padded curtain treatment can affect the handle of lightweight fabrics, particularly sheers. Pile fabrics treated from the back retain their face pile character if the treatment does not penetrate the face. Any fabric where colour or handle change would be commercially significant should be sample-treated and approved before committing to a full order.

Who can issue a Crib 5 certificate?

Only a UKAS-accredited testing laboratory can issue a Crib 5 certificate. A fabric supplier, treatment company, or interior designer cannot self-certify FR compliance. When specifying a fabric for contract use, request the test certificate from the supplier and confirm that the issuing laboratory is UKAS-accredited. For contract curtain treatment requiring BS 5867 Part 2 Type B, the same applies.

For how back-coating and wet padding work, see our how FR treatment works guide. For the fire standards requiring FR treatment, see our Crib 5 guide. For dye types and their interaction with FR treatment, see our dye types and FR treatment guide.