What's inside it

You can only judge about a fifth of a sofa by looking at it. The fabric, the shape and the stitching are on the outside; the frame, the suspension and the foam are the parts that decide whether it still looks like this in eight years, and all three are hidden under the upholstery by the time you meet it.

This is what is under there, what the differences actually do, and how to form a decent opinion in a showroom in about two minutes. It applies to any sofa from anyone — buy on it here or somewhere else.

The frame

The frame is the skeleton, and it is the component whose failure ends a sofa. Foam can be replaced and covers can be re-upholstered. A frame that has cracked or worked loose at the joints is usually the end, because the labour to fix it exceeds what the sofa is worth.

Broadly, three tiers, and the differences are real:

• Solid hardwood, kiln-dried — beech, birch, ash. Kiln-drying is the part that matters as much as the species: timber that still holds moisture shrinks in a heated house, and joints that were tight in the factory work loose over a winter or two. This is the top tier and it is priced like it.
• Plywood and engineered timber — genuinely good, and unfairly dismissed. Decent multi-ply is dimensionally stable, resists splitting along a grain because it has no single grain, and is what a great many perfectly sound sofas are built from.
• Particle board and chipboard — the bottom. It holds a screw once. It does not hold one again after the joint has flexed a few thousand times, and it fails badly rather than gradually when it gets damp.

How the frame is joined matters at least as much as what it is made of. You want joints that are glued and dowelled or screwed, with corner blocks bracing the angles. Staples alone, holding structural joints rather than just the fabric, are the single clearest sign that a frame was built to a price.

What actually holds you up

Between the frame and the cushion is the suspension, and it is doing more work than anything else in the sofa. Three common systems:

• Elasticated webbing — woven straps stretched across the seat frame. Light, cheap and comfortable when new. It relaxes over time, and a seat that has begun to sag in the middle is very often webbing rather than foam, however much the foam gets blamed.
• Serpentine springs — also called sinuous or zig-zag: lengths of shaped steel running front to back. The workhorse of the industry, and the right answer for most sofas at most prices. Firmer than webbing and far more durable.
• Pocket springs — individual coils in fabric sleeves, the same idea as a good mattress. Each responds independently, so the seat supports you unevenly in the way a body actually is uneven. The most comfortable and the most expensive.

None of these is wrong. A serpentine-sprung seat at £600 is a sensible piece of engineering, not a compromise; pocket springs at that price would mean the money came out of the frame or the foam instead.

Seat foam, and the only number worth knowing

Foam is sold on two different measurements and people routinely confuse them.

Density — kilograms per cubic metre — is how much material is in the foam. It is the durability number. Roughly: around 20–25 kg/m³ is budget and will soften noticeably inside a couple of years; 30–35 is a solid domestic seat; above about 35 is high quality and will hold its shape for many years.

Firmness is a separate measurement entirely, and a dense foam can be soft while a cheap one can feel hard. This is the trap: a budget sofa often feels firm and supportive in a showroom precisely because low-density foam has not been sat on yet. Six months of daily use is what tells the two apart, which is exactly when it is too late.

Density is the number to ask for. If a retailer cannot tell you, that is itself a data point — though not always a damning one, since plenty of honest shops simply have not been told by their own supplier.

Backs, and where a cheap sofa shows first

Back cushions are usually filled with polyester fibre, foam, feather, or a mix. Fibre is soft and inexpensive and flattens; foam holds its shape and feels firmer; feather is the most luxurious and needs the most plumping.

The back is where age shows first, because nothing about a flattened back cushion is structural — so it fails quietly rather than obviously, and a sofa can look tired for reasons the owner never diagnoses. A fixed high-back holds its shape without any help; a scatter-back needs plumping and will look neglected within weeks if it does not get it. Neither is better made. One asks more of you.

The cover, and why it matters less than you think

Upholstery fabric is rub-tested on the Martindale scale, which counts how many cycles of abrasion the cloth survives. As a rough guide, general domestic use is served from around 15,000–25,000 rubs and heavy domestic use from about 25,000 upwards; the very high figures quoted in marketing exist for offices, bars and hotels.

The honest version is that for a sofa in a house, almost any competent upholstery fabric will outlast the frame it is stretched over. Fabric choice is far more about how it behaves — whether it wipes clean, whether it shows every mark, how it takes light — than about whether it will wear through. That is the subject of the fabric guide, which goes through all six of ours properly.

Judging one in two minutes

You will not be shown a cutaway. You can still learn a surprising amount by handling it:

• Lift one front corner. A well-built sofa is heavy, and the whole front rail should come up as one piece. If the frame twists or you hear a creak, the joints are not doing their job.
• Sit on the front edge. Right on the rail, not back in the seat. You should feel a solid edge, not a bar digging in and not a void.
• Press the arm firmly from the side. Arms take an enormous amount of abuse — people sit on them — and a soft or shifting arm means it is padding over something thin.
• Look underneath. Lift the dust cover if you can. You are looking for proper joints and corner blocks rather than a grid of staples.
• Sit in it for longer than feels normal. Five minutes, not thirty seconds. Comfort in the first ten seconds is upholstery; comfort at five minutes is suspension and foam.

What to ask, including us

Four questions get you most of the way with any retailer:

1. What is the frame made of, and is the timber kiln-dried?
2. What is the seat suspension — webbing, serpentine or pocket springs?
3. What is the seat foam density in kg/m³?
4. What exactly does the guarantee cover, and for how long?

We can answer the fourth precisely and in public: one year, covering structural faults in the wooden frame and the springs, on every sofa we sell. Not wear and tear, not fading, not accidental damage — the structure. Some of our pieces are also made in the UK, and those carry a Made in the UK badge on their product page rather than a general claim across the range.

For the first three on a specific sofa, ask us about that piece. We would rather check with the maker and tell you the real answer than publish a number across the whole range that turns out not to be true of the sofa you bought. If you want to press on the arms and sit on the front rail yourself, the Blackburn showroom is open by appointment.

A last word on price

None of the above means the most expensive construction is the right purchase. A kiln-dried hardwood frame with pocket springs and 35 kg/m³ foam is a genuinely better object, and it is also the correct choice for perhaps a minority of buyers — the ones keeping a sofa for fifteen years in a busy family room.

For a spare room, a first flat, or a room whose layout you expect to change, a sound frame with serpentine springs and mid-density foam is not a compromise. It is the right amount of sofa. The mistake is not buying cheap; it is buying cheap while believing you bought something else.