EVA foam
Dense, closed-cell and firm. It holds a cut edge precisely, which makes it the material for a ring slot, a watch cushion core or any seat that has to keep its shape under weight.
It does not compress much, so a slot cut in EVA is exactly the size it is cut to. That is a virtue when the dimensions are right and a problem when they are not.
Polyethylene foam
Lighter and softer than EVA, and cheaper. It suits a pad under a lining where the job is cushioning rather than holding — a flat bed for a mixed piece, or the base of a cavity.
It takes a knife edge less cleanly, so it is the wrong choice where a cut edge will be visible through a thin lining.
Wadding and fibre fill
Soft, loftable and used where the interior has to look padded rather than engineered — a domed pad, a plump cushion, a traditional ring bed.
It compresses over time under a heavy piece, which is why a steel watch bracelet is better on an EVA-cored cushion than a wadded one.
How a seat is actually built
A typical interior is a board tray, a foam layer cut to the shape, and a lining wrapped over both. The lining you see is doing almost none of the holding.
That is why the same-looking velvet interior can be firm in one box and soft in another — the difference is under it.
Choosing by weight and use
Heavy pieces and boxes that will be opened for years want EVA. Light pieces and gift boxes opened once are fine on softer fill, and it feels more generous.
At a glance
| Material | What it is for |
|---|---|
| EVA | Slots, cushions and any seat that must hold its shape |
| Polyethylene | Cushioning pads and cavity bases |
| Wadding | A padded look — domed pads and plump cushions |
| Board tray | The structure everything else is built on |
Frequently asked questions
What is under the velvet in a ring slot?
Usually EVA foam cut to the shank. The velvet is the surface; the foam does the holding.
Why does my cushion flatten over time?
Almost always a wadded cushion under a heavy piece. An EVA-cored cushion holds its shape under a steel bracelet.
Can you make a firm interior look soft?
Yes — an EVA core with a wadding layer over it reads soft and holds its shape. That is a common specification.
Do you use plastic foam in every box?
No. Board and paper interiors do the same job for many pieces, and we will say when a piece genuinely needs a moulded or foam seat.
Tell us what you need
Tell us the piece, your brand and the quantity you have in mind. We’ll send photos of our work and one clear, all-in quote.