Glossary · Property

3D printing

Hygroscopic

A material is hygroscopic if it absorbs moisture from the air. Many filaments do this and then print worse.

Explained in more detail

Almost all filaments absorb water from the air, and how much depends on the plastic. Particularly hygroscopic are PA (nylon), which according to Prusa can absorb up to 10% of its weight in water, and water-soluble PVA. In the hotend the water evaporates suddenly: it crackles, bubbles and strings appear, the surface becomes rough and layer adhesion weakens. Drying reverses this in most cases. Afterwards the filament should be stored airtight with desiccant.

Where does the term come from?

From Greek hygros, "moist". In chemistry, the word describes substances that bind water vapour from the surroundings, for example silica gel, which is also used as desiccant in filament boxes.

In practice

• Crackling, more strings and rough surfaces during printing are typical signs of damp filament.
• Store opened spools in an airtight box with desiccant; under 20% relative humidity is a good guideline.
• A hygrometer in the box shows when the desiccant is exhausted.
• Nylon and PVA are best printed straight from a drybox.
• When drying, stay below the softening temperature of the material, otherwise the windings stick together on the spool.

Not to be confused

Hygroscopic does not mean water-soluble: nylon absorbs water but does not dissolve. PVA is both, which is why it serves as a water-soluble support material.

Frequently asked questions

Which filament is the most hygroscopic?

Among common filaments, mainly PA (nylon) and PVA. According to Prusa, nylon can absorb up to 10% of its weight in water, and even a few hours open in the room worsen print quality.

Do I have to dry PLA as well?

PLA absorbs less water than nylon, but after long open storage it also prints worse and becomes brittle. Drying at 45 to 55 °C for 4 to 6 hours helps.