Moulding materials compared

At a glance

First four columns: general trade knowledge, to be confirmed by partners. Last column: what the documents we read say; no class is claimed for any product.

Six materials, one section

A moulding is a shape, and the material decides how it behaves once it is on the wall. The six below cover most of what a schedule will name. The drawing uses one section, an S-curve of the kind used for a dado cap or a small cornice, so that only the material changes. The shapes themselves are on our moulding profiles sheet.

• Hardwood is solid timber from broadleaved trees such as oak, walnut or cherry. It is dense, takes a clear or stained finish and can be sanded back and re-finished. It moves with the humidity of the room, so mitres and returns can open; the timber movement sheet works the arithmetic.
• Softwood is solid timber from conifers such as pine, spruce or fir. It is easy to work and stocked in standard profiles. Knots and resin can show through paint, and it dents more easily than most hardwoods.
• MDF is board pressed from wood fibre and resin. It machines to a crisp profile with an even face for paint, and it moves less than solid timber but still moves. It swells if it is wet, and moisture-resistant (MR) board is not waterproof. The MDF decoded sheet sets out the grades.
• FR MDF is MDF made with a fire-retardant treatment so that it can carry a stated reaction-to-fire class. The class is stated for the board as tested, at a thickness and mounting, and a finish or a different fixing can change it.
• Plaster mouldings are gypsum, cast in a mould or run in place with a profile template. They give the long crisp runs of a period cornice, but they are heavy, they crack where joints or the building move, and they need a plasterer to fix and fill.
• Polyurethane mouldings are moulded rigid foam with a harder skin. They are light and can be curved or made in large sections. The detail can be less crisp, and the generic fire lists we read have no entry for them.

Timber is not one thing

Hardwood and softwood describe the tree, not how hard the timber is. The chart takes side hardness, the force needed to press a steel ball into the face, from the US Forest Products Laboratory’s Wood Handbook (2021, Table 5-3a, wood at 12 per cent moisture), with density from Table 4-6a. Oak is hard. Yellow-poplar, a hardwood, is softer than Douglas-fir, a softwood. The softest timbers here take about a quarter of the load that white oak does (1,600 N against 6,000 N).

For a rail that meets chair backs, trolleys and bags, name the species. The figures are for US-grown species: European and imported timbers differ, so ask the partner’s timber supplier for figures on the timber actually used. Density matters a second time for fire, because the generic list for solid timber starts at 390 kg/m³ (see below), and it is the lightest softwoods that fall under it.

MDF has no species. In the US Architectural Woodwork Standards (1st edition, 2009), a comparison of panel cores rates MDF excellent for visual edge and for surface uniformity, and good for dimensional stability. That is a table for panel cores, not a moulding test, but it fits the usual reason for choosing MDF: a clean face to paint.

Mouldings and fire in England

In England, Approved Document B sets classes for the surface linings of walls and ceilings (Volume 2 paragraph 6.1 and Table 6.1; Volume 1 paragraph 4.1 and Table 4.1). Paragraph 6.3 (Volume 1: 4.3) says a wall does not include doors and door frames, window frames, architraves, cover moulds, picture rails, skirtings and similar narrow members, or fireplace surrounds, mantle shelves and fitted furniture. For ceilings, paragraph 6.6 (Volume 1: 4.6) leaves out architraves, cover moulds, picture rails, exposed beams and similar narrow members. The edition is the 2019 one incorporating the 2020, 2022, 2025 and 2026 amendments, read in November 2026.

So the usual narrow mouldings, in any of the six materials, are outside the Table 6.1 classes. Two things stay in. The wall or ceiling behind them is still a lining. And the lists do not name cornices, coving, dado, chair or plate rails, or applied panel mouldings, and “similar narrow members” is not defined. Whether a deep cornice or a run of applied mouldings counts is for building control or the fire engineer to say, in writing. Scotland, Wales and Northern Ireland have their own guidance, which we did not read.

When a class is needed, the route depends on the material. Three generic lists, in EU Decisions retained in UK law and published on legislation.gov.uk, name products that can be classified without further testing. Approved Document B points to such lists (Appendix B, paragraph B6) and also says a result holds only for the product as used: small differences in fixing, joints, dimensions and air gaps can change it (paragraphs B2 and B8).

A board that fits the lists reaches class D, not C or B. D-s2,d0 and D-s2,d2 both meet the D-s3,d2 asked for in a small room, but not the C-s3,d2 asked for in other rooms or the B-s3,d2 asked for in other circulation spaces. Our fire performance of wall panelling sheet reads Table 6.1 and works through what that means. The lists name types of board, not products, and a finish, a veneer adhesive or a fixing detail is outside what they say.

Choosing by setting

There is no rule that fits every room. These are starting points, with the question to settle before the schedule is fixed.

Specifying a moulding so the right material arrives

• Name the material fully. “Hardwood” or “MDF” is not a specification. Write the species and grade, or the board type, thickness and the document it comes with.
• Draw the section at 1:1. The profile sheet explains why a name never fixes a size.
• Say where the fire question applies. Narrow members are outside the wall list; a cornice, a rail or a panel moulding may need an answer from building control. Put that answer on the drawing.
• Where a class is needed, require the document. A Declaration of Performance or classification report for the moulding as installed, not a material name.
• Seal every face and end. This matters most for MDF and timber in a damp room. The finishes sheet covers the systems.
• Mock one run up. Fix one length with its returns and finish before the run is made.

We coordinate the moulding drawing, the choice of material and any mock-up with the partner workshop that will produce the work, before the schedule is fixed.

Ref [M-01]: [skirting / dado rail], profile as detail [D-12] at 1:1, [120 x 25] mm finished. Material: [oak, dried to [ ] per cent moisture content] / [softwood, species [ ], paint grade]. Finish [ ]. Seal all faces and ends before fixing. The drawn section governs over any catalogue name.

Ref [M-02]: [skirting] moulding, profile as detail [D-12] at 1:1. Board: MDF to BS EN 622-5 [type MDF / MDF.H], [ ] mm thick, supplied with a Declaration of Performance. Primed and finished [ ]. All faces and cut ends sealed. Substitution only with the designer's written approval.

Ref [M-03]: [cornice], profile as detail [D-20] at 1:1, in [plaster, run in place / cast] / [polyurethane]. [Cornices, rails and applied mouldings] to be confirmed by [building control / the fire engineer] in writing as [outside / inside] the lining classes. Where a class is required, supply the Declaration of Performance or classification report for the moulding as installed.

Standards and sources

• Approved Document B Volumes 1 and 2 (England), 2019 edition, amendments to 2026: Vol 2 paras 6.1 to 6.6; Vol 1 paras 4.1 to 4.6; Appendix B.
• Decisions 2003/43/EC (amended by 2007/348/EC), 2006/213/EC, 96/603/EC: legislation.gov.uk.
• BS EN 13501-1:2018 and BS EN 622-5:2009: current on BSI Knowledge; not read.
• USDA Wood Handbook FPL-GTR-282 (2021): Tables 4-6a, 5-3a.

Questions we are asked

Is MDF or solid timber better for skirting boards?

Neither is better in every room. MDF gives an even painted face and a crisp profile for a modest cost, while solid timber takes knocks better, can be re-finished and moves with humidity. In a damp room, seal every face and end of either. The choice is about the room, the finish and the knocks it will take.

Do skirting boards need a fire rating in England?

Approved Document B leaves skirtings, architraves, cover moulds, picture rails and similar narrow members out of what counts as a wall (Volume 2 paragraph 6.3; Volume 1 paragraph 4.3; 2019 edition with amendments to 2026). The wall behind is still a lining and must meet Table 6.1. Scotland, Wales and Northern Ireland have separate guidance.

What does FR MDF mean?

MDF made with a fire-retardant treatment so that it can carry a stated reaction-to-fire class. It is not the same as fire-resisting construction, which is how long a door or wall holds. The class belongs to the board as tested, so ask for the Declaration of Performance and check it covers your thickness, substrate and finish.

Is a plaster cornice non-combustible?

Gypsum and gypsum-based plasters are on the Commission list of materials classed A1 without testing, if the product is made only from listed materials with no more than 1.0 per cent homogeneously distributed organic material. A casting that includes fibre or timber reinforcement may not qualify, so ask the plasterer what it contains and for evidence.

Is polyurethane moulding fire rated?

We found no entry for polyurethane in the three generic lists we read. Ask the maker for a classification report for the moulding as installed, and ask whether the material counts as a thermoplastic under Approved Document B Appendix B paragraphs B10 to B13, which treat such materials separately.

Which timber is best for a rail that takes knocks?

A dense one. The Wood Handbook gives white oak about 6,000 N side hardness against about 1,600 N for western redcedar, and yellow-poplar, a hardwood, is softer than Douglas-fir, a softwood. Name the species in the schedule and ask the supplier for figures on the timber used.