Sinuous Springs and Elastic Webbing

Modern supports

Through the 20th century, factories replaced hand-tied coil springs with faster systems: serpentine (sinuous, zigzag) springs and elastic webbing, topped with polyurethane foam instead of hair, and fastened with staples instead of tacks ¹. Most furniture made today is built this way, and it’s what you’ll find under most mid-century and modern seats.

Sinuous springs

A sinuous spring is a heavy wire bent into a continuous zigzag and formed into an arc. Strips run from the front rail to the back rail (or side to side on deep seats), held by clips nailed or screwed to the rails, and arc slightly upward, so the seat is crowned.

Installing them:

1. Measure front-to-back between clip positions and cut each strip to length with bolt cutters or a spring cutter, cutting so each end can be bent into a hook.
2. Bend the ends with pliers or a bending tool so they hook into the clips.
3. Fasten the clips to the rails at even spacing, padded with a strip of felt or burlap so the wire doesn’t click against metal.
4. Hook in the springs, one end first, then stretch and seat the other end.
5. Tie them together: helical springs or tie wires running side to side, or spring twine tied across like coil springs, so they act as one platform and don’t twist or let one strip sag on its own.
6. Cover with burlap (or a heavy insulator pad) so the foam doesn’t push down between the wires.

Use the spring gauge and arc specified for the piece; replacing a broken strip with a matching one is a common repair.

Elastic webbing

Elastic (rubber) webbing is stretched across a frame like jute webbing, but it’s resilient on its own, so it can replace springs in thin seats and backs:

• Stretch it a set percentage (often specified by the webbing maker) and staple or clip it to the rails.
• Run strips one way or interlaced both ways.
• Cover with foam directly.

It’s light, thin, and quiet, and suits Danish modern chairs and slim sofa backs. It loses elasticity over decades and is replaced, not repaired.

Comparing supports

Hand-tied coils remain the mark of top-quality seating; sinuous springs and elastic webbing make sense in modern frames designed for them. Don’t mix systems blindly: a frame built for coil springs has deep rails and a bottom for webbing; a sinuous frame has stout front and back rails to hold the clips.

Repairing

• Broken or popped-out sinuous spring: refasten the clip with longer screws, or replace the strip with one of the same gauge and length.
• Sagging elastic webbing: replace all strips at once so tension is even.
• Squeaks: add padding under clips and between wires and frame.

The coil-spring principle still applies: sagging is often a fastening or tying failure, not a broken spring ².

What to take from this

Modern seats use sinuous (zigzag) springs clipped front to back, tied together side to side, and covered with burlap, or elastic webbing stretched across thin frames, with foam on top. They’re quick and shallow; hand-tied coils are deeper and more conforming. Match the support to the frame, replace springs with matching ones, and check fastenings before blaming a spring.