The catalogue can't cover what you actually need.

Between any two SKU sizes, say a 1200mm panel and a 1500mm panel, there are an infinite number of widths a real wall might be. 1247mm. 1318mm. 1399.5mm. The catalogue can't list them all because there isn't a catalogue long enough. So it picks a step and rounds. Every panel supplier does this. It's how catalogues work.

The contractor specifying acoustic for a real room runs into this on every job that isn't a new-build with off-the-plan dimensions. The room is what it is. The wall is 2,847mm. The catalogue's nearest panel is 2,400mm, leaving a 447mm strip the contractor has to fill, badly, with an offcut. Or 3,000mm, forcing a panel that overruns and has to be cut on site, with a fibrous edge the client can see from across the room.

The catalogue isn't wrong. It's just finite. And the wall isn't.

Ordinary rooms, not unusual ones.

The places where catalogue maths breaks aren't unusual rooms. They're ordinary rooms.

A meeting room in a converted Victorian building has a ceiling height of 2,712mm and a soffit running across the back wall at 2,340mm. Standard panel sizes are designed for new-build dimensions. Neither one fits. The contractor either picks the closest size and accepts the visible gap, or orders custom and the room is finished cleanly.

A partition layout in a fit-out doesn't divide into 600mm increments. The room is 4,180mm wide, the door takes 900mm, the run of acoustic to the door is 3,280mm. Three 1,200mm panels gives 3,600mm and a butchered offcut. One 3,280mm panel gives a clean wall.

A column in the back of a conference room. A bulkhead concealing services. A sprinkler head, a beam, a cable tray, a light fitting that someone else specified six months ago and that the acoustic now has to live around. Every one of these forces a cut. The question is whether the cut is made in a factory, by someone who does it for a living, with a CNC tool and a clean edge, or on site, by hand, on the morning of the install, with a Stanley knife and a tape measure.

The wall that looks fitted, not finished.

A wall that should have been a single panel ends up as three panels with two visible joins. The joins line up where the panels meet, not where the room's geometry would have them. The client sees them.

A panel that needs to wrap a column gets cut on site. The factory edge meets the site-cut edge. The factory edge is clean. The site-cut edge is not. Both are now on the same wall.

Two panels that should match exactly come from different production runs because the catalogue size was out of stock when the rest of the order shipped. They're both grey. They're not the same grey. The contractor notices when fitting the second one. The client notices the next morning.

Each of these is a small thing, individually. Together they're the difference between a wall that looks finished and a wall that looks fitted.

What it actually costs to cut on the day.

The standard response to catalogue mismatch is we'll just cut it on site. It's the default reflex because it's how most acoustic gets handled, and because for years it's been the only option a catalogue supplier offered.

Look at what site-cutting actually costs.

It costs an installer's time on the day, when they're trying to finish before the client walks the room. It costs a clean edge, which a Stanley knife on PET felt cannot produce. It costs offcut waste, which the contractor either disposes of or carries back to the yard. It costs the option of the panel ever being moved or reused. Once it's cut to that wall, it's that wall's panel.

And it costs the conversation with the client when they ask why the edges don't look like the website photos.

Custom-fabricated panels avoid every part of that. They arrive cut to the millimetre. The edge is the factory edge, the same edge as every other panel in the room. The fit is the spec. The labour cost on the day is fitting, not measuring and cutting.

For most jobs, custom is also faster end-to-end. The hour saved on site usually outweighs the lead time, because the lead time happens before the install date, when no one's standing on a site waiting.

What changes when the supplier holds the spec.

The deeper question isn't whether the panels fit. It's who carries the awkwardness when they don't.

When a contractor orders catalogue panels and cuts them to fit, the contractor owns the result. If the joins are visible, that's the contractor's joins. If the edges are rough, that's the contractor's edges. The client looks at the contractor and asks why it doesn't look better. The contractor explains that the catalogue panels weren't quite the right size. The client doesn't really care about catalogue panels.

When the contractor specifies the wall and the supplier fabricates to that spec, the supplier owns the fit. If something is wrong, it's between the contractor and the supplier, not between the contractor and the client. The contractor's job is the install. The supplier's job is delivering panels that fit the room as measured.

This is the actual product being sold. Not panels. Risk transfer. The contractor stops being the buffer between the catalogue's limitations and the client's expectations.

Specify by millimetre, not by SKU.

Specify by millimetre, not by SKU. The wall is 2,847mm wide. The panel is 2,847mm wide.

Cut around fittings, not just on flat walls. Sprinkler heads, cable trays, light fittings, beams, bulkheads. Geometry that accommodates the services already on the wall, made in a factory rather than negotiated on site.

Match a brand-spec colour, not a stock palette. Where the client's brand needs a specific colour and the standard 17 won't do it, custom-batch.

Curve, angle, taper, radius. Where the room geometry demands it. Where a flat panel would be a compromise.

Custom isn't an upcharge for trade buyers, the way it is for retail. It's how the order gets specified in the first place. The catalogue is a starting point for buyers who want to start there. Trade buyers usually don't.