Paper pulp: why a vessel made of paper holds water

What paper pulp consists of

The raw material is used paper, often the offcuts from ongoing production. It is soaked or boiled until the fibre bond dissolves, drained and mixed with a binder. The mash goes into a mould, releases water and dries out. What remains is a firm, porous body of matted cellulose fibres.

Anyone who has ever made papier-mâché knows the principle. The difference lies in the execution, and it is greater than it sounds.

Two processes, two completely different results

Papier-mâché, French for chewed paper, has been made in two ways since the 15th century. In the strip method, strips of paper are layered on top of one another with paste. This produces large, robust bodies, but thick walls and an uneven surface. In the pulp method, the paper is first broken down completely into a mash and formed in one go.

The wall thickness is then no longer created by layers, but by the density of the fibre mash and the time the mould stands in it. That is exactly why today's pulp vessels are thin-walled and smooth, where papier-mâché remained clunky. Industrially, the same process is called moulded fibre. It is in every egg box and every seed tray.

Drying takes place in an oven. If the still damp body is pressed between heated moulds, the surface and dimensions become considerably more precise; drying with circulating air alone leaves a coarser skin and larger tolerances. You can see this on the surface of a piece.

Why the fibre is in the right place here

A cellulose fibre can be recycled about five to seven times. With each cycle it breaks a little further, becomes shorter and binds less well – at some point it is no longer good enough for quality paper. That does not make it worthless. It remains suitable for everything that tolerates short fibres: cardboard, egg boxes, moulded fibre.

That is the point at which a pulp vessel is made. It is not a substitute for a better material but the last use a fibre can still serve before it ends up in general waste.

How a vessel made of paper can hold water

The answer is on the inside. A thin layer of natural latex, obtained from the milky sap of the rubber tree, covers the fibres and closes the pores. The effect is measurable: a coating of natural rubber latex reduces the moisture absorption of paper from around 21.6 to about 0.15 per cent. At the same time, it improves the barrier against oxygen and water vapour.

In practice this means: fresh flowers are possible, water stays in the vessel. That does not make the vessel indestructible. The layer is thin and sits on a substrate that absorbs by nature. If it is damaged, that spot is exposed.

Where the material reaches its limit

Two things affect paper pulp, and both are predictable.

The first is light. Natural rubber is broken down by UV radiation and oxygen; heat and moisture accelerate this. For water-repellent coatings in general, UV is considered the most common reason why the effect wears off after weeks to months rather than after years. A piece like this therefore belongs indoors and not on the terrace, and indoors not in full south-facing sun either.

The second is moisture from outside. Inside, the vessel is sealed; outside, it is paper, and paper is hygroscopic. It absorbs moisture from the air and releases it again in order to reach equilibrium with its surroundings. The fibres swell by 15 to 20 per cent in the process. A permanently damp bathroom is therefore the wrong location, a normally heated living space the right one.

How long the inner sealing actually lasts in a living space is an open question. There are no reliable figures on this, and anyone who gives one has made it up. What can be said: without direct sun and without mechanical damage, little happens to the layer.

Care: what helps and what harms

Care follows directly from the construction. Wipe it with a dry or slightly damp cloth; nothing more is needed. Soaking, holding it under running water or putting it in the dishwasher destroys the substrate from the outside – no inner sealing helps against that.

If you use it for fresh flowers, change the water regularly and let the vessel dry in between. For planters without a drainage hole: either use them as a cachepot or water sparingly. Standing water over weeks is the only strain that really attacks such a piece from the inside.

Scratches and knocks leave marks that cannot be polished away. On the other hand, nothing breaks. A piece that falls off the shelf is dented but still stands. That can rarely be said of ceramics.

The weight, and what it changes in a room

A vessel made of paper pulp weighs less than half of a comparable ceramic piece of the same size. A round cachepot of just under twenty centimetres (7.9 in) in diameter stays under half a kilogram (1.10 lb); the same in ceramic comes in at double that and more.

A light object can be placed on a shelf that would be too weak for stoneware. It can hang. It can be moved without two people carrying it. And it looks lighter when a room already carries a lot of mass: natural stone on the table, solid wood on the wall, a heavy rug.

The drawback is the other side of the same property: a tall, narrow vessel made of paper stands less stably than one made of clay. Where children or animals pass through the room, a squat shape is the wiser choice.

Where the material comes from

A large share of the pieces made of paper pulp are produced in Sri Lanka, from locally collected paper waste. They are formed by hand, and that has two consequences: dimensions vary by millimetres, and no two pieces turn out exactly the same. With a material whose entire appeal lies in the slightly irregular surface, this is not a defect but the reason it looks good at all.