This glossary explains the terms that appear in enquiries, drawings and test reports for bent wood parts. The definitions come from the shop floor rather than from a dictionary: every value is what we actually control in running production.
Materials and species
Bentwood
Timber that has been plasticised by steam and formed into a permanent curve. Covers both solid bent wood and bent plywood.
Solid bent part
A component made from one continuous piece of timber. The grain runs unbroken around the curve, so the breaking load is higher than in laminated alternatives.
Bent plywood
Several thin veneer layers bent and glued together. Allows much tighter radii than solid wood because each layer is strained only slightly.
Laminated wood
A semi-finished part glued from several veneer or board layers. Used when parts are longer than one natural piece or have to be especially stable.
Moulded wood
Wood-based part pressed in a heated tool with a three-dimensional shape. Unlike steam bending, the contour comes from pressure and temperature, not from a bending form.
Ash
Fraxinus excelsior. The classic bending timber: elastic, easy to plasticise, straight-grained and light in colour. The standard for chair frames.
Beech
Fagus sylvatica. Around 720 kg/m³, fine even texture. Takes tight radii reliably and is the benchmark for volume chair frames.
Birch
Betula pendula. Bends cleanly and veneers well, but reacts badly to over-steaming and then tends to tear.
Walnut
Juglans regia. Dark, decorative grain. Chosen when the visible surface carries the design; slightly stiffer to bend than ash or beech.
Grain direction
The direction of the wood fibres in the part. It must run parallel to the bend line, otherwise cross-grain tension causes cracks on the outer curve.
Process
Steam bending
A process in which timber is heated in saturated steam and bent over a form while still warm. The form is held until the part has cooled and dried.
Plasticising
The loss of stiffness caused by heat and moisture. The lignin matrix between the cellulose fibres softens so the fibres can slide over each other.
Lignin
A natural component of wood that surrounds and bonds the cellulose fibres. It softens during steaming and fixes the new shape as it cools.
Conditioning
Deliberately setting the moisture content before steaming. The target is around 20 to 25 percent, so the fibres plasticise without tearing.
Steaming time
Duration of the steam treatment, depending on section thickness. A working value is about 15 minutes per centimetre — a 20 mm section needs roughly five hours.
Steel strap
A flexible band that wraps and compresses the outer curve during bending. It prevents the outer fibres tearing in tension and allows tighter radii.
Bending form
The tool that defines the target contour. Made per part and archived for the life of the programme so repeat orders are identical.
Clamping
Fixing the bent part on the form. The part stays clamped until it has cooled and dried back to service moisture.
Springback
The elastic recovery of a part after it is released from the form. Compensated by over-bending, longer clamping and slow drying.
Press bending
Forming in a heated tool under pressure. Faster and more repeatable than steam bending for thin sections and all laminates.
Construction and tolerance
Bend radius
The inner radius of the curve, measured on the inside of the part. It determines whether a section can be bent at all.
Radius-to-thickness ratio
Radius divided by part thickness. With a steel strap the practical limit is about 2:1, without about 5:1.
Cross-section
Shape and size of the part perpendicular to its length. Rectangular sections bend more evenly than strongly profiled ones.
Wall thickness
Part thickness across the bend line. Thin walls allow tighter radii but buckle more easily on the inner curve.
Tolerance
Permitted deviation from nominal size. On machined dimensions after drying we normally hold plus/minus 0.5 mm.
Template
A checking gauge that reproduces the target contour as a negative. Every batch is checked against it, because a tape measure does not capture curvature.
Tension zone
The outer side of the curve where fibres are stretched. Cracks start here when bending without a strap or with timber that is too dry.
Compression zone
The inner side of the curve where fibres are compressed. Buckling appears here when the wall is too thin.
Cracking
Separation of fibres on the outer curve. Causes are low moisture content, over-steaming, or too tight a radius without a strap.
Buckling
Rucking of the inner curve through compression. Occurs when the radius is tighter than the section allows, or clamping pressure is too high.
Testing and quality
Case-hardening
Hardening of the outer zones through drying too fast. The outer layers shrink before the core, creating internal stress and hairline cracks.
Moisture content
Water content as a percentage of dry mass. Bending targets 20 to 25 percent; the finished part is set to the equilibrium of the target market.
Equilibrium moisture content
The moisture level a part settles at for a given temperature and humidity. For Central Europe this is typically 8 to 11 percent.
Visual inspection
Visual check of every batch for cracks, pressure marks, glue lines and colour variation. It supplements dimensional inspection, not replaces it.
Dimensional inspection
Measurement of radius, section and length against drawing and template. The basis for releasing a batch.
EN 1728
European standard for the stability, strength and durability of seating furniture. Relevant for chair frames and seat shells.
BIFMA
US standard for office furniture with defined load cycles. Requested by North American clients in addition to EN.
Formaldehyde
A binder component in wood-based materials. Since August 2026 the EU limit is 0.062 mg/m³ for furniture and wooden articles under REACH Annex XVII.
FSC and PEFC
Certification schemes for sustainable forestry. Clients generally require an unbroken chain of custody back to the sawmill.
EUDR
EU deforestation regulation, applicable from December 2026. Requires species, country of origin and geolocation of the plots for wood products.
Commercial
MOQ
Minimum order quantity per part. It follows geometry and tooling effort rather than a fixed figure, and is stated in every quotation.
Tooling
The bending or press form made for a part. Built to drawing and archived in-house for the life of the programme.
First sample
The first part from production tooling, submitted for approval. Series production starts only after approval.
Lead time
Time from an approved drawing to shipping readiness. Typically 7 to 15 days for samples and 15 to 30 days for production orders.
EUDR: What importers need for their due diligence statement from December 2026 is summarised under EUDR and bent wood.