Seat suspension systems compared

At a glance

Cost class is a relative order for a like-for-like seat (labour and materials, not prices); the partner workshop confirms the order for the actual build. Feel and use are typical practice, not figures from a standard.

What the suspension does

A seat is built in layers: cover, wrap, foam, then the suspension on the frame. The foam sets how the surface feels on the first sit. The suspension sets how far the seat gives under the body, how evenly it comes back and how it ages. The foam, wrap and cover are on the foam and feather sheet; this sheet is about what is underneath.

Where a seat is deep and relaxed, springs do most of the work. Where it is thin or formal, the foam does, and the base under it is webbing or a board. That is why the drawing draws the foam thicker as the springs disappear. The suspension is also hidden once the cover is on, so it can be changed without anyone noticing, which is the reason to name it in the specification.

The five systems

1. Eight-way hand-tied

Tall tapered coil springs stand on webbing across the seat rails (the frame timbers that the suspension is fixed to). Each spring is tied to its neighbours and to the frame with laid twine in eight directions (front to back, side to side and both diagonals), so the springs are held upright and move as one bank. Hessian (a coarse woven cloth) goes over the tops, then stuffing, wrap and foam. Comfort: the deepest, slowest and most progressive give of the five, with an even recovery. Durability and repair: it is made by hand and mended by hand: the seat can be stripped and re-tied, and the fill and cover renewed, without replacing the frame. The twine and the ties are what age. Watch for: it needs the most depth under the cushion and the most labour, and the name is used loosely (see the inspection section).

2. Sinuous springs

Continuous S-shaped steel wire, running front to back (sometimes side to side), fixed to the rails with clips and cross-tied so the wires keep their spacing. Foam sits over a hessian or similar layer that protects it from the wire. Also called serpentine, zig-zag or no-sag springs. Comfort: firmer and more immediate than hand-tied, with less depth, so it suits a slimmer, more contemporary seat. Durability and repair: fewer parts and no twine; a worn wire or clip is replaced rather than re-tied. Watch for: the wire size, the number of wires and cross ties, and the thickness of foam over them are set by the workshop, so ask for them to be named.

3. Pocket springs

Each coil is sewn into its own fabric pocket, and the pockets are joined into strips or a unit that sits on a board, or is built into the cushion itself (a spring-interior cushion, see seat cushion constructions compared). Comfort: even and buoyant, because each coil moves on its own and the surface follows the body. Durability and repair: there is no twine or clip to loosen; the pocket fabric and the joins between pockets are the parts to ask about, and a unit is replaced as a unit. Watch for: the depth of the unit, how it is fixed to a rigid base, and the foam or fibre layer above it.

4. Webbing

Straps woven across the seat rails: jute (traditional, and the base under hand-tied springs), elastic or synthetic. Foam or a thin wrap sits directly on top. Comfort: light, springy and shallow, with the most give in the middle of the span, which suits a slim or tailored profile. Durability and repair: the lightest-duty of the five: webbing stretches and perishes with age, and a tired seat is re-webbed. Watch for: the span between rails and heavy contract use.

5. Foam deck

A rigid base, usually plywood or a similar board fixed to the frame, with foam on top. There is no spring: the foam is the only cushioning, so its density, hardness and thickness (see the foam sheet) are the specification. Comfort: flat, firm and even; a softer top foam or a fibre or feather wrap relaxes it, but it cannot give as deeply as springs. Durability and repair: the board does not sag; wear shows as foam losing thickness and firmness, and the foam is replaced when it tires. Watch for: foam quality is everything, and the fire route is the composite of cover, interliner and foam.

Durability, repair and what to ask the workshop to name

None of the five is a certificate, and the specification should not say only “sprung seat”. The table says what usually ages first, how it is repaired and what to ask the workshop to name in the build.

Where strength and fire tests fit

Strength and durability testing of seating used outside the home is done on the whole seating item to BS EN 16139. On BSI's listing its scope does not cover upholstery durability, ageing or flammability, so it tells you how the chair as made behaved, not how long a spring system or foam deck will last, and not which system is better. Fire evidence belongs to the composite of cover, interliner and filling: see BS 7176 hazard categories and the fire documentation matrix. Ask the workshop to confirm that the build they supply is the build that was tested.

Which system for which seat

These are typical choices, not rules. The partner upholsterer confirms what suits the frame, the seat depth and the use, and which systems they build. For how geometry, fill and cover change the character of a seat, see formal versus relaxed seating.

• Heavy daily use. Ask the workshop which builds they stand behind for contract use, and agree the warranty terms for the seat as a whole at the outset, on the same sheet as the build.
• Repair. A seat that can be re-tied, re-webbed or re-foamed in place costs less to keep than one that must be replaced. Ask what can be renewed without removing the frame.
• Prototype. Feel is the point of the suspension, so approve it on a full-spec prototype: see the sit-test protocol.

How to inspect, and how to tell a true hand-tied seat from an imitation

A finished seat hides its suspension, and several different builds are sold as “sprung” or even “hand-sprung”. Pressing a showroom seat shows firmness, not construction. The reliable evidence is documents and photographs from the workshop, taken before the cover goes on.

• Ask for the build in writing: the system, the type and number of springs or wires, how they are fixed and tied, the base, and the foam on top.
• Ask for build photographs or a cut-away sample of the exact build, with a scale in shot, for each seat type, and to inspect the first production item before it is covered.
• Look underneath. Lift the dust cover. A hand-tied seat shows coils standing on webbing; a sinuous seat shows continuous wire. The twine is on top of the springs, under the hessian, so it cannot be seen from below: only a photograph of the tied springs, or an open seat, shows it.
• Ask how the springs are held. A prefabricated unit fixed in a few places is not hand-tied. If a workshop calls a seat hand-tied, it should be able to say how many springs there are and how they are tied.
• Check the cost. Hand-tied is the highest cost class because the labour is the cost. A price that sits close to a sinuous seat deserves a question.
• Check the same build on every item: the prototype, the first production item and the delivered seat.

Seat suspension: [eight-way hand-tied / sinuous springs / pocket springs / webbing / foam deck on board] as shown on the build-up section [drawing ref, revision]. Not to be changed or substituted except by written variation approved by the designer.

Eight-way hand-tied: [tapered coil springs, [ ] per seat, shown on the shop drawing] fixed to [jute] webbing across [ ] mm seat rails, each spring tied to its neighbours and to the frame with [laid twine] in eight directions, to a [flat / slightly crowned] height of [ ] mm above the rails, covered with [hessian] before stuffing and wrap. Photographs of the tied springs to be provided before covering.

Sinuous springs: [ ] mm wire [size stated by the workshop], [ ] wires per seat at [ ] mm centres running [front to back], fixed to the rails with [steel clips] at both ends and cross-tied with [ ] ties per wire. [Hessian or insulator pad] over the springs before the foam.

Seat base: [jute / elastic / synthetic] webbing [ ] mm wide at [ ] mm centres, woven in both directions and fixed to the rails with [ ]. OR: seat base: [ ] mm [plywood] deck fixed to the frame with [ ], with foam to the foam specification [ref].

For each seat type, before production: a cut-away sample or build photographs showing suspension, fixing, foam and cover with a scale in shot, and inspection of the first production item before it is covered. Photographs filed with the shop drawing.

Standards and sources

• No standard defines these five systems: trade descriptions; no figure for springs, wire or webbing is given.
• BS EN 16139:2025: Non-domestic seating, safety, strength and durability. BSI listing: current. Tests the seating item; scope excludes upholstery durability, ageing and flammability.
• BS EN 1728:2012: Seating, test methods for strength and durability. BSI listing: test methods only.

Questions we are asked

What does ‘eight-way hand-tied’ mean?

A seat suspension in which tapered coil springs stand on webbing and each spring is tied to its neighbours and to the frame with twine in eight directions: front to back, side to side and both diagonals. The tying holds the springs upright and makes the bank move as one, giving a deep, slow, progressive give. It is the most labour-intensive system, so it sits in the highest cost class.

Is hand-tied better than sinuous springs?

It gives deeper and slower support and costs more, but better depends on the seat. Hand-tied suits a deep, traditional seat; sinuous suits a slimmer, firmer one, and a well-built sinuous seat is a sound choice for heavy use. A badly built hand-tied seat is not better than either, which is why the build should be named and photographed.

Are pocket springs suitable for contract seating?

They can be. Each coil moves on its own and there is no twine or clip to loosen. Ask for the build, the depth of the unit and how it is fixed to a rigid base, and ask the workshop and spring supplier whether that unit suits heavy daily use; this sheet gives no figure for it.

Does a foam deck count as suspension?

It is a seat base rather than a spring: a rigid board with foam on top, so the foam is the only cushioning. It stays flat and is simple to renew, and it is a common choice for fixed banquettes and many contract chairs. Because the foam does all the work, its specification matters most.

How can I tell if a sofa really is hand-tied?

You cannot tell from the finished piece. Ask the workshop for the build in writing and for photographs of the tied springs before covering, or a cut-away sample. Lifting the dust cover shows coils on webbing, but the twine is on top of the springs, so only a photograph or an open seat shows it.

Does the suspension affect the fire certificate?

Fire evidence belongs to the composite of cover, interliner and filling. Ask the workshop and the test laboratory whether the base or suspension was part of what was tested, and that the build supplied matches the build tested. See the BS 7176 and fire documentation sheets.

What should I write in a specification?

Name the system and its build on the build-up section, ask for build photographs for each seat type, and say that the suspension may be changed only by written variation. The wording above has a line for each system.