Why Sofa Cushions Sag, And What's Really Going On

You're probably blaming the wrong part

When a sofa starts to sink, everyone reaches the same conclusion. The cushions have gone. So they get flipped, rotated, restuffed, sometimes replaced altogether. And a few weeks later the dip is right back where it was.

Here's the thing. The cushion usually isn't what failed. The cushion is sitting on something, and that something is what gave up.

What's actually under there

Pull your seat cushions out and look at the flat seat base underneath. Depending on how your sofa was built, you'll find one of three things.

Elastic webbing

Wide rubbery straps stretched across the frame in a criss-cross pattern. Very common in mid-range and flat-pack furniture, because it's cheap, light and genuinely comfortable when it's new. It's also elastic, and elastic wears out. After a few thousand sit-downs those straps stretch and stop pushing back.

Sinuous springs

S-shaped steel wires running front to back. You might hear them called zig-zag or no-sag springs. Tougher than webbing, and you'll find them in better-built sofas. They still lose tension over the years, and the ones under the middle seat go first.

Coil springs

Individual coils tied together, usually in older or higher-end pieces. These last a long time. When they do fail it's normally a tie coming loose rather than the whole system going soft.

Why the middle always goes first

Because that's where people sit. In a three-seater the centre seat gets the most use, and the support under it has to span the widest gap with nothing to help it. The ends have the frame and the arms nearby taking some of the load. The middle has webbing and that's it.

Which is why a sofa can look completely fine from across the room and still swallow you when you sit down in the wrong spot.

How to work out what's failed

Take the cushions out and press down hard on the bare seat base with your hand.

• It gives easily and stays low. The webbing or springs have stretched. That's the common one, and it's fixable.
• It feels firm but the cushion still collapses. The foam has broken down. New foam or new inserts will sort it.
• You hear a scrape, or something feels loose. A spring has come off its clip, or the frame has shifted. That's a repair job.

Most people find the first one.

What you can do

Reupholstery will replace that webbing properly. It'll also cost you several hundred dollars and take your sofa away for a week or two. For a sofa you were already half thinking about replacing, that's a hard sum to justify.

The other option is to stop trying to bring the elastic layer back and just put something rigid on top of it. A solid board laid across the seat base gives your cushions a flat surface that doesn't move. The tired webbing is still down there. It's just not the thing holding you up any more.

That's what our boards do. There's nothing clever about it, and that's exactly why it works.

When it won't help

Be honest about what you found under those cushions. If the frame is cracked, or a spring has snapped, or the cushions are fixed down and won't come out, a board on the seat base isn't the answer and no amount of it will be.

But if the seat base just feels tired, and on most sofas past five years old it does, that's the exact problem this solves.