PVA and BVOH: printing soluble support material correctly

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Some models can hardly be printed with normal supports: internal cavities, nested parts or overhangs that no tool can reach. Water-soluble support materials help here. You print the supports from PVA or BVOH, put the finished part in water, and the supports dissolve.

Requirement: a printer for two materials

Soluble supports need a printer that can process two materials in one print. There are three ways to do this:

• Tool changer or two nozzles: Each material has its own nozzle. This is the cleanest solution, because the materials do not mix.
• Multi-colour system with one nozzle: The filament is swapped, and the nozzle has to be purged each time. This works, but costs time and material. Residue of the build material in the support material can make later dissolving harder.
• Only the contact layer soluble: Many slicers can print only the top support layer directly under the model from PVA and the rest from the build material. This saves expensive support material and swaps.

Which devices can handle several materials is shown in the overview Multi-colour printers. The basics of supports in general are in the article Supports.

PVA and BVOH compared

The values are guide values. Prusa gives 195 °C for its PVA and 215 °C for BVOH. The values on the spool take priority.

PVA is the classic, more widespread support material. It is somewhat cheaper, but clogs more easily and is very delicate with moisture.

BVOH adheres better to the build material, dissolves faster and tolerates a little more humidity. It costs more, though.

Which materials does it work with?

What matters is that build material and support material are printed at similar temperatures and adhere well to each other.

• PLA: the best combination for PVA and BVOH. The temperatures match well.
• PETG: possible with some PVA and BVOH types, check according to the manufacturer’s specification.
• ABS, ASA, PA, PC: For PVA, the printing and chamber temperatures of these materials are usually too high. BVOH works with some engineering materials, and for ABS and ASA there are also dedicated support materials, such as HIPS, which dissolves in limonene.

A tip from Prusa: do not print PVA and BVOH directly on the build plate, but on one or two layers of PLA raft. This improves adhesion noticeably.

Storage: extremely sensitive to moisture

PVA and BVOH are made to dissolve in water. Accordingly, they absorb moisture from the air quickly. After only a short time open in the room, the filament becomes soft and sticky, prints badly and can clog the nozzle or the multi-colour system.

1. Dry before printing, typically at 45 to 55 °C for several hours. Details are in the article Drying filament.
2. Keep dry during printing, ideally printing from a dry box or a dryer.
3. Immediately after printing, put it back in an airtight container with desiccant.
4. Buy small spools. PVA and BVOH often come on 500 g spools. That makes sense, because a large spool will hardly stay dry to the end.

Dissolving: how it works

1. Remove the bulk first. Remove beforehand whatever can be easily broken off or pulled out with pliers. This saves a lot of time.
2. Put in water. Lukewarm water speeds up dissolving considerably. For parts made of PLA, no warmer than about 35 °C, otherwise the PLA can deform. Never above 50 °C.
3. Agitate. Stirring, a container with a pump or running water shortens the time. An ultrasonic cleaner helps too.
4. Be patient. Depending on amount, temperature and agitation, it takes from under three hours to overnight.
5. Change the water. Saturated water dissolves more slowly. For large amounts, use fresh water. As a rough guide, Prusa gives about 20 ml of water per gram of BVOH.
6. Rinse and let dry.

PVA is biodegradable. According to the manufacturers, the water can go down the drain if it is connected to a sewage treatment plant. Afterwards, rinse briefly with warm water.

Cost: is it worth it?

Soluble support material costs many times as much as PLA per kilogram. Added to that are the purge waste with single-nozzle multi-colour systems and the longer print time. For most prints it is therefore too expensive. It makes sense for parts that cannot be made cleanly without soluble supports, or only with great effort.

The cheaper alternative: supports made of a different material

Often it is enough if the support and the part do not stick to each other. PLA and PETG, for example, bond poorly to each other. If you print the contact layer of the support from PETG and the part from PLA, the support can be peeled off cleanly and the underside becomes smooth. This also works the other way round.

Some manufacturers also offer special, non-soluble support materials that deliberately adhere poorly to PLA or PETG and can be broken off. Here too it is usually enough to print only the contact layer from them.

Continue with: Multi-colour printing.