It is a very fine abrasive - the hard cell walls of the foam cut the mark off the surface, using water only as a lubricant.

The foam has an open structure whose walls are rigid and, at microscopic scale, sharp-edged. Drawn across a surface, those edges act like extremely fine abrasive particles.

Water softens the residue and lubricates the action; it plays no chemical role.

This is why it removes marks that no detergent shifts - scuffs, crayon, pen and transferred rubber are physically removed rather than dissolved.

It also explains the limitation: a very fine abrasive still removes surface material, and repeated use in one place will show.

Adding chemical does not help and can attack the surface while the foam works mechanically - water is the correct medium.

Scuffs and transferred marks on painted walls, crayon and pen on paintwork, residue on switch plates, and hard water marks on tiling and glass.

Rubber transfer from shoes, trolleys and furniture is the classic application. Detergent cannot dissolve it; melamine cuts it off.

Crayon, pencil and many pen marks on painted surfaces respond immediately, which makes it a standard item in schools and childcare.

Scuffs on skirtings, door frames, corridors and lift interiors are the volume use in hospitality and healthcare.

Mineral deposits on tiling, shower screens and taps respond because the marks are physically removed rather than needing acid.

Its usefulness in occupied buildings is partly that it needs no chemical, so there is no odour, no residue and no ventilation requirement.

Gloss and high-sheen finishes, polished surfaces, some paints, printed markings, acrylic and clear plastics, and vehicle paintwork.

Gloss paint and lacquered surfaces are dulled - a matt patch appears exactly where it was used, and it cannot be restored by cleaning.

Some emulsion paints, particularly cheaper matt finishes, are removed along with the mark, leaving a lighter patch.

Printed markings on appliances, switch plates and control panels are abraded away, often before the operator notices.

Acrylic, polycarbonate and clear plastics scratch and haze.

Vehicle paint and any automotive clear coat should never be treated with it, despite the frequent suggestion otherwise.

The rule is: test on an inconspicuous area, use light pressure, and stop as soon as the mark has gone.

Because the foam is the abrasive - it is consumed as it works, and crumbling is normal rather than a defect.

Each pass wears away cell walls, which is exactly the mechanism by which the mark is removed. The pad gets smaller and sheds fine particles.

A pad used on a rough surface disappears very quickly; on smooth paintwork it lasts longer.

Once it has shrunk to the point where it cannot be held, it is finished. There is no way to restore it.

Cutting a block into smaller pieces avoids wasting a large pad on a small mark and is standard practice.

Wipe the surface afterwards - the shed particles are left behind and are visible on dark surfaces.

Damp, not soaking, with light pressure, in one area at a time, testing first and stopping as soon as the mark clears.

Wet the pad and squeeze out the excess. A dripping pad marks walls and runs down them.

Light pressure is more effective than heavy. Pressing hard accelerates both the removal of the mark and the damage to the surface, and it wears the pad out faster.

Work in small areas and check progress frequently, because the transition from clean to damaged is not always obvious while working.

Test in a hidden place on any painted or finished surface before starting.

Wipe the area with a damp cloth afterwards to remove shed foam particles and any loosened residue.

Gloves are worth wearing for prolonged use; the foam is drying to the skin.

It leaves no chemical residue, which is an advantage, but surfaces should still be wiped and the pad kept out of reach as with any cleaning item.

Because it works with water alone, there is no detergent residue to rinse off, which is one reason it is used in schools, nurseries and healthcare.

Shed foam particles are left behind and should be wiped away, particularly on food surfaces.

The pads are not a food-contact cleaning tool in themselves and should not replace proper cleaning and sanitizing of food surfaces.

They look like sponges and are sometimes mistaken for them, so storing them with cleaning equipment rather than in a kitchen drawer avoids confusion.

Follow the manufacturer's safety information as with any product, and keep them out of reach of small children for the same reasons as any cleaning consumable.

For marks that resist normal cleaning, yes - it removes in seconds what would otherwise need repainting. For general cleaning, it is an expensive way to wipe a surface.

Per pad, melamine foam costs considerably more than a sponge and lasts far less time.

Against that, a corridor of scuffed walls restored in an hour avoids a decorating job, which is where the value lies in hospitality, healthcare and education.

Using it for routine cleaning wastes it - a cloth and detergent does that job for a fraction of the cost.

Buying in bulk blocks and cutting to size is substantially cheaper than pre-cut branded pads and is what most commercial operations do.

Treat it as a specialist item on the trolley for the marks nothing else shifts, and the economics are strongly favourable.