Upholstery Inside Out: Frame, Springs, Foam, and Cover

Upholstery is architecture you sit on. The cover receives attention because it is visible, but the chair’s behavior comes from a layered system below it.

The National Park Service describes upholstered furniture as a composite of frame, support, springs, fillings, cover fabrics, trimmings, tacks, and adhesives ¹. Those layers move against one another. They also fail on different clocks.

Read the stack from the floor up

Frame

The frame establishes geometry and carries loads. Solid wood, plywood, laminated veneer lumber, steel tube, cast aluminum, and molded polymer can all make good frames.

Inspect:

• joinery and reinforcement at the front rail, back posts, and arm junctions;
• whether fasteners bite into adequate material;
• diagonals or corner blocks resisting racking;
• smooth edges where webbing or fabric passes;
• access to re-tighten or replace parts;
• whether the decorative outer form corresponds to structure.

A heavy frame is not automatically strong. Strategic section depth, grain direction, joints, and bracing matter more than mass alone.

Deck and suspension

The deck closes the seat structure and isolates layers. Above or within it, support may come from:

• jute or synthetic webbing, tensioned across a frame;
• sinuous springs, clipped in parallel;
• coil springs, tied to control vertical and lateral movement;
• elastomeric straps, offering quiet, controlled compliance;
• molded shells or flexible slats, where the structure itself deflects.

Traditional eight-way hand-tied coils demand substantial fitting and knotting. They can distribute loads beautifully and be repaired. They are not automatically superior in a shallow modern lounge chair where a tested elastomeric support or shaped shell better matches the geometry.

Cushion core and comfort layers

Polyurethane foam comparisons are often muddled. The Polyurethane Foam Association distinguishes ²:

• density: polymer mass per unit volume;
• firmness or IFD: force needed to indent the sample under a defined method;
• support factor: how resistance rises at deeper compression;
• resilience: spring-back behavior;
• flex fatigue: change after repeated compression;
• tensile, tear, and compression-set behavior: resistance to particular damage or lasting deformation.

Density is not firmness. A higher-density foam can be formulated soft; a lower-density foam can feel hard at first. Higher polymer content often helps retain properties, but formulation and test data still matter.

Layering lets a maker tune the response:

• firmer base foam prevents bottoming;
• softer top foam distributes local pressure;
• fiber or wool wrap softens edges and fills the cover;
• feather or down creates enveloping comfort but needs containment and regular redistribution;
• latex can offer lively resilience and long service, with cost, weight, and allergy or sourcing considerations;
• horsehair, cotton, coir, wool, or other traditional fillings behave differently and require skilled shaping.

Cover and seams

The show cover must survive tension, flex, body oils, light, spills, cleaning, and rubbing against its own seams. Specification can include fiber, weave, backing, finish, width, repeat, pilling, seam slippage, breaking or tear strength, colorfastness, and flame requirements.

The Association for Contract Textiles publishes minimum physical guidelines for indoor woven upholstery ³. Its caution is crucial: one test cannot predict all field performance. An enormous abrasion number does not tell you whether a loose weave will snag, dye will transfer, a seam will slip, or the fabric feels appropriate.

Why patterned upholstery consumes fabric

Fabric is purchased by length at a fixed width. Solid or non-directional cloth can often be nested efficiently. A directional motif or large repeat forces the cutter to align pattern landmarks.

Maharam’s specification pages illustrate the variables: width, horizontal repeat, vertical repeat, and whether a design is railroaded ⁴.

Railroaded means the pattern is oriented to run along the roll rather than up its width in the conventional direction. It can allow a long sofa back to be covered without a vertical seam—but only when the motif, weave, stretch, and manufacturer’s use guidance allow it.

A rough yardage model is:

required fabric = net pattern area ÷ layout yield + repeat-matching allowance + defect/re-cut allowance

Matching stripes across a T-cushion, centering a medallion on a back, and making a pair of chairs mirror each other can consume much more cloth than surface area suggests.

Upholstery labor is subtraction and prediction

Before a new cover appears, a restorer may need to:

1. photograph and mark every panel;
2. remove trim, tacks, staples, cover, padding, and support without damaging the frame;
3. diagnose old repairs and structural movement;
4. rebuild webbing, springs, or edge rolls;
5. create or correct patterns;
6. estimate how new foam and cloth will compress;
7. cut with grain, direction, and repeat control;
8. sew curved boxing, corners, zippers, and relief cuts;
9. tension the cover evenly without distorting pattern;
10. finish the underside and preserve access for future work.

The skill is predictive. Cloth that appears loose on the bench may tighten around a compound curve. Foam that feels perfect bare may become too firm under a low-stretch cover.

Three quality levels

Public or lounge seating can also be tested as a finished product. ANSI/BIFMA X5.4 addresses safety, durability, and structural adequacy ⁵. That evidence answers different questions from textile abrasion or foam density.

A chair audit without cutting it open

1. Lift one front corner: does the frame rack or creak?
2. Press the seat slowly: note initial softness, deeper support, edge support, and bottoming.
3. Stand up: observe recovery after one minute and again later.
4. Feel below the deck for webbing or springs without forcing the dust cover.
5. Inspect seams at the front edge and arm where load changes direction.
6. Check pattern centering and matching.
7. Find zippers, removable panels, screws, clips, labels, or other repair access.
8. Ask for frame, suspension, foam, textile, cleaning, and test specifications separately.

Rule of thumb

Do not buy upholstery by squeezing the top inch. Read the stack, the transitions, and the repair path. Great upholstery feels simple because many hidden layers were made to cooperate.