Nobody talks about the foundation. That's why most re-upholstery work is a disappointment by year six.
The client brings in a tired piece. The upholsterer puts new fabric on it. The piece looks right. It doesn't feel right. The foundation — everything between the frame and the cover — never got touched.
Between the wood and the fabric: springs, webbing, foam, batting. That stack determines how the seat feels, how long it holds its shape, and whether the piece is still worth sitting in a decade from now. The client chooses the fabric. The client lives in the foundation.
Springs
Two types. Not interchangeable.
Coil springs are the benchmark. Individual springs tied to the frame rail at eight points each — that's why quality upholstery is called eight-way hand-tied. Each spring moves independently. Load distributes across the full seat depth, recovers evenly, stays consistent across the surface. It takes longer to build. It's worth it for any seat that will see daily use.
Sinuous springs — no-sag springs — are S-curved steel wire clipped to front and back rails. Faster and cheaper. Fine for backs and light-use seating. The failure mode is specific: after about eight years, the middle of the span loses tension. The soft spot lands exactly where most people sit. It's not obvious at year two. It's the first thing a client complains about at year eight.
Elastic webbing as a primary support system belongs on occasional-use chairs. It's not a daily-seat foundation.
The Platform
Above the springs, below the foam: jute webbing interlaced across the deck. It carries load, absorbs movement, distributes stress away from the springs' attachment points. Properly installed, it doesn't need replacing every time the seat is rebuilt.
Poorly installed — not enough tension, too few strips, cheap material — it's the first thing that fails.
Foam
Density and ILD are two different things. Most people treat them as one.
Density is mass per cubic foot. It determines durability — how long the foam holds its structure before it breaks down. ILD (Indentation Load Deflection) is firmness — how the foam actually feels under load. You can have dense soft foam, dense firm foam, lightweight soft, lightweight firm. All four combinations exist. The cheap stuff tends to be low-density, which is why it feels hard and collapses faster. Both failures at once.
Minimum spec for residential daily use: 1.8–2.0 lb/ft³ density, 25–35 ILD for seat surfaces. For anything that will genuinely get used: 2.5 lb/ft³ HR foam with an optional comfort layer. HR stands for High Resilience — open cell structure that breathes, compresses under load, and recovers. It doesn't just compress and stay there.
Batting
Dacron fills the gap between cut foam and finished fabric. Without it, the rectangular edge of the foam block telegraphs right through the cover. You can see the shape of the foam under the fabric. With dacron, the seat reads as continuous. Rounded. Finished.
This is the layer that separates a seat that looks like upholstery from a seat that looks like foam in a bag.
Correct residential seat build: HR foam at the right ILD, comfort layer if specified, full dacron wrap. That's the floor.
The Conversation
Before scope, before fabric, before anything: tell the client what the foundation needs. Four areas — springs, webbing, foam, batting. If the foundation is degraded, you say so. If you recover without addressing it, the piece looks restored and feels wrong.
The honest line: "The fabric is the last decision. The foundation is the first. If the foundation needs work, we do it first, or the result won't last."
Get the foundation right and the piece is rebuild-able indefinitely. Let it degrade and every subsequent re-cover is temporary relief.
They'll call you again because the seat still feels right at year ten. Not because the fabric was beautiful.