PVA vs HIPS: Soluble Supports for PLA, PETG and ABS

This week’s Monday piece covered multi-color printing with the AMS and how much filament and time every color change eats up. Soluble supports are the other side of the same coin: they run on identical material-swap mechanics, but instead of looks they solve geometry you could not otherwise print in one piece. PVA dissolves in water, HIPS in limonene, and the choice of solvent is exactly what decides which support fits which main material. This article works through material pairings from the documentation of three manufacturers (which contradicts itself in one spot), then moisture as the most common cause of PVA failure, PrusaSlicer and Bambu Studio settings, the dissolving itself, and finally the question of when soluble supports are not worth it.

What sets PVA and HIPS apart, and what dissolves them

PVA is polyvinyl alcohol, a soft and strongly hygroscopic polymer. UltiMaker’s technical data sheet lists a glass transition temperature of 58.4 °C, a melting temperature of 175.4 °C and a density of 1.23 g/cm³ for PVA. It dissolves in ordinary water, with no solvents and no fume extraction, and it is biodegradable in natural fresh water with no hazardous byproducts.

HIPS is polystyrene with rubber additives. Prusa recommends a nozzle temperature of 225 to 255 °C and a bed of 100 to 110 °C, the same range ABS runs in. It dissolves in limonene or acetone. Compared to ABS it is lighter and shrinks far less, so large supports print more calmly.

The difference between water and limonene is not a detail. Water is free, it is everywhere, and a bucket will do for a container. Limonene is an oily organic solvent that stays on the surface of the model even after it dries; the part smells of citrus for a long time afterward, and Prusa quotes a minimum drying time of 24 hours for chemical smoothing. The solvent is therefore the first decision, not the last.

Which support belongs to which material

The safest combination is PLA with PVA. Bambu Lab lists PVA as a support for PLA and for the filled PLA-CF and PLA-GF variants; Prusa allows both PVA+ and BVOH with PLA. The temperatures of the two materials overlap, adhesion works, and the bath is nothing but lukewarm water.

With PETG the confusion starts. In its general guide to support filaments, Bambu Lab states that PVA is not compatible as a support filament for printing in PETG. For PETG, Prusa recommends practically only BVOH, which it describes as stiffer, easier to print and more expensive than PVA+. UltiMaker, on the other hand, lists good adhesion to PLA, PETG and nylon for its PVA in the technical data sheet. And Prusa’s HIPS page names supports for large PETG models as its best use.

You will find the contradiction inside a single brand as soon as you start reading the documentation for a specific machine. For the H2D, Bambu Lab clarifies that PVA and PETG should not be printed at the same time from the left and right nozzle: PVA has a low heat deflection temperature, and when the bed is heated to 70 °C for PETG, the nozzle clogs easily. The same page adds, however, that with the AMS and a single nozzle, PETG with PVA supports can be printed. So it is not the material pair that makes the difference, but the machine configuration.

ABS and ASA have the classic pairing with HIPS, but there is a catch here too. In its article on water-soluble materials, Prusa names HIPS as the best alternative for printing ABS with soluble supports. On the separate HIPS page it says the opposite: it is not suitable for supports for ABS and ASA, because those materials partly dissolve in limonene as well. With Prusament ASA Orange, according to Prusa, this damages interlayer adhesion and the model falls apart into small flakes. The practical answer is to keep the part out of the bath: dip it briefly, loosen the supports and pull them off by hand.

What does not work matters just as much. UltiMaker lists its PVA as unsuitable for supports for ABS, CPE+, PC and PP. The temperature range of these materials is too high for PVA, and the material degrades in the nozzle before it does its job.

• PLA and PLA-CF or GF: PVA, or BVOH, with a lukewarm water bath
• PETG: according to Prusa practically only BVOH; with Bambu Lab never in the two hotends of the H2D and not at all in the general guide, with HIPS as the limonene alternative
• ABS and ASA: HIPS, but no long soaking, because limonene attacks the part itself
• Nylon: according to the UltiMaker data sheet PVA holds well; Bambu Lab has its own Support for PA and PET
• PC, PP and CPE+: the manufacturer does not recommend soluble PVA supports

Why manufacturer documentation disagrees

The PETG contradiction is not one manufacturer’s mistake. PVA is not a single material but a family. Prusa writes about PVA+, elsewhere BVOH is sold, a copolymer of butenediol and vinyl alcohol, and every formulation has different thermal stability and different adhesion to the neighboring material.

The machine plays a role too. Bambu Lab judges combinations from the perspective of the AMS, where all filaments pass through one nozzle and mix in a single hotend. UltiMaker tested PVA on dual extrusion with two separate nozzles, where the materials only meet on the model. A manufacturer’s recommendation therefore holds for the setup it came from, not universally.

Only one sensible rule follows: go by the documentation for your specific trio of main material, support and machine, and verify it on a small part with a twenty-minute print. Not on a fourteen-hour print where the failure will really sting.

You can quickly check whether your setup is AMS-compatible below.

Moisture decides whether PVA runs at all

PVA takes on water faster than any common filament, and that is the main reason it fails for people. Bambu Lab gives concrete numbers: in a dry environment up to 20% relative humidity, dried PVA stays usable for one to three days, while in an ordinary room at around 55% humidity a freshly dried spool absorbs enough moisture within one to three hours to degrade print quality. A normal interior sits somewhere between 45 and 65% relative humidity.

Drying is therefore not an optional step. For PVA, Bambu Lab recommends a hot air dryer at 80 °C for 8 to 12 hours, a heated bed at 90 to 100 °C for 12 hours, the AMS 2 Pro at 65 °C for 18 hours and the AMS HT at 85 °C for 18 hours. Move the spool somewhere dry right after drying, without waiting for it to cool down, or it will pull part of the moisture straight back.

Not all desiccants are equal either. For PVA, Bambu Lab recommends calcium chloride, noting that silica gel will not keep the material dry long term, and advises holding humidity below 20% in the AMS. For PVA+ and BVOH, Prusa insists on returning the spool to a bag with silica gel immediately after printing, because otherwise the filament degrades over a few months, starts softening at a lower temperature and causes trouble as early as loading. Best of all is to print and store straight from a drybox.

You can tell the state of the filament by bending it. Dry PVA is stiffer than PLA Basic; damp PVA softens and gets sticky. Softened filament deforms in the AMS Lite, which is why Bambu Lab does not recommend PVA in the open AMS Lite, avoids it entirely on the A series, and on other machines advises keeping such prints under an hour.

HIPS is the relaxed material in this respect. For its Support for ABS, whose main component is HIPS, Bambu Lab states that it is not moisture sensitive and usually needs no pre-drying.

• Dryer: 80 °C, 8 to 12 hours
• Heated bed under a cover: 90 to 100 °C, 12 hours
• AMS 2 Pro: 65 °C, 18 hours; AMS HT: 85 °C, 18 hours
• Storage: airtight box with calcium chloride, target below 20% relative humidity

Slicer settings: this is where consumption is decided

For MMU3, MMU2S and XL profiles at 0.15 and 0.2 mm layer height, PrusaSlicer offers two extra presets, SOLUBLE FULL and SOLUBLE INTERFACE. The first prints the entire support structure from soluble material and suits complex internal structures. The second uses soluble material only in the contact layers between support and model, with regular filament carrying the rest. That saves the more expensive material.

Prusa points out a detail here that will save you a pile of scrap: PVA+ and BVOH stick poorly to both smooth and powder-coated PEI sheets, while they grip PLA and PETG well. If the support stands directly on the bed, SOLUBLE INTERFACE is the safer choice.

The second item is nozzle purging. A standard filament change uses 140 mm³; for soluble supports Prusa recommends at least 200 to 240 mm³, and a change out of PVA+ or BVOH may need a minimum of 240 mm³. The purge tower grows just as it does with multi-color printing, only this time you are not paying for color but for a clean transition.

Budget for time as well. Prusa lists a maximum volumetric speed of 15 mm³/s for PLA, while PVA+ and BVOH manage 4 mm³/s. Every layer with support therefore takes longer than you are used to.

In Bambu Studio, PVA is set under Process, Support, Filament for Support, both as support base and as support interface. For PVA, Bambu Lab recommends avoiding tree supports, because tall thin structures made of a softer material fall over, and using the classic grid instead. It gives a nozzle temperature range of 240 to 250 °C.

For MMU2S and MMU3, PrusaSlicer assigns the support material to filament number 5 by default, and to tool 2 on the XL. A value of 0 means whatever is currently loaded gets used, which only makes sense for prints without changes.

How to actually dissolve the supports

For PVA, Prusa recommends submerging the finished print in warm water at a maximum of 45 °C and leaving it there for several hours or overnight. Before the bath it pays to snap off as much support as you can while it is dry. After you pull the part out, let the remnants soak another 10 to 20 minutes and brush them away with a stiff toothbrush.

Bambu Lab states that dissolving takes hours to tens of hours, and that warm water plus agitation speeds the process up. It also warns that with PLA models the water should not exceed 50 °C, because the part starts to deform. Water also finds its way through interlayer gaps into internal cavities, so with closed volumes expect the model to dry for a few days after you take it out.

HIPS needs limonene. For chemical smoothing, Prusa gives a 10 to 20 second dip and a minimum of 24 hours of drying, and the citrus smell lingers on the model for a long time. For supports on ABS or ASA the same warning applies as above: a short dip, loosened supports and mechanical removal beats leaving the part in the bath all night.

Disposal is easy with water. Prusa states that unless you are dissolving kilograms of PVA or BVOH a day, you can pour the resulting solution down the drain, and UltiMaker describes PVA as biodegradable in natural fresh water. Handle limonene according to its safety data sheet; it does not belong in the sink.

• Remove as much support as you can dry, before the bath
• PVA: water up to 45 °C, never above 50 °C for PLA models, several hours to overnight
• Agitation or a small pump cuts the time far more than higher temperature does
• HIPS: a short dip in limonene, then mechanical removal, 24 hours of drying

What soluble supports cost on top

The cost has three parts, and filament is the smallest of them. Soluble materials are more expensive than PLA and PETG, which is exactly why Prusa created the SOLUBLE INTERFACE preset that uses soluble material only where it matters.

The second part is time. A 4 mm³/s ceiling, 200 to 240 mm³ of purge at every change, an extra purge tower, and then hours of soaking or a whole day of drying with limonene. A print that would take an afternoon in a single material stretches overnight.

The third part is operation and safety. For Support for ABS, Bambu Lab warns that it releases styrene at printing temperatures, and recommends an enclosed printer, a well-ventilated room and a vapor-filtering mask for long prints. For the same material it adds that a 0.2 mm nozzle is not recommended and that variable layer height can crash the print. Soluble supports are not a set-and-forget mode.

When to use them and when to skip them

Soluble supports pay off where mechanical removal would be impossible or would ruin the surface. Typically that means internal channels, closed cavities, thin fine details and assemblies printed in one piece. With them the support-to-model distance can be set to zero, so bottom surfaces come out smooth, which regular supports cannot do.

For simple overhangs, rough prototypes and mechanically tough parts, on the other hand, snapping the supports off is faster. It is likewise not worth touching PVA without a dryer or drybox, because on open systems the odds that the filament goes damp before the print finishes are high.

A short test before the real part saves the most. Print a small sample with the same material combination, dissolve it, and only then start the big model.

• Use: internal channels, closed cavities, fine details, articulated assemblies in one piece
• Use: parts whose bottom surface has to be smooth, with no support marks
• Skip: simple overhangs and sturdy prototypes where snapping them off is enough
• Skip: printing without a dryer or drybox, especially on open systems

Soluble supports are not one material or one setting. PVA solves with water what HIPS solves with limonene, and between them sits BVOH for PETG plus a whole range of proprietary formulations whose recommendations always apply to a specific setup. Start with PLA and PVA on a small part, verify drying and purge, and only then start the model where it matters. And before you trust a universal compatibility table, read what the maker of the filament actually on your spool says about your combination.

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