Vacuum forming with 3D-printed moulds: sheet, master, process
are explained briefly when you hover over or tap them.
In vacuum forming, a plastic sheet is heated, laid over a mould and sucked tight against it by negative pressure. The mould is called a master, tool or template. A 3D printer makes a good vacuum forming tool: the master is printed in a few hours and can be adapted as you like. For it to work, three things count: a master that withstands the heat and can be demoulded, the right sheet for the purpose and air that can escape everywhere.
How vacuum forming works
Mayku describes the process in five steps:
- Design and make the master, for example by 3D printing.
- Clamp the sheet. It lies in the frame over the forming bed.
- Heat the sheet until it is soft. Mayku advises watching for the moment the sheet just starts to sag.
- Lower the sheet over the master and apply vacuum. The pump sucks out the air between sheet and master, and the sheet hugs it tightly.
- Let it cool, demould, trim.
There are two kinds of master. A positive master (Mayku: “male”) is raised, and the sheet lies over it on the outside. A negative master (“female”) is a recess, and the sheet is drawn into it. According to Mayku, positive masters are more common in vacuum forming, above all for casting moulds for chocolate, soap, candles or Jesmonite and for simple packaging. The side of the sheet that touches the master is always the dimensionally accurate one.
The 3D-printed master
Material and heat
To form, the sheet becomes considerably hotter than a printed part can withstand permanently. Formech gives forming temperatures of 120 to 160 °C for PETG, 150 to 175 °C for HIPS and 150 to 180 °C for ABS. The master only gets the heat briefly, but still deforms if the material softens too early or heats up over several runs in a row.
| Filament for the master | Heat deflection temperature per data sheet | Assessment for vacuum forming moulds |
|---|---|---|
| PLA | HDT 55 °C (Prusament PLA) | Formech: low heat resistance, only for a quick prototype. Mayku: needs high infill. |
| PETG | HDT 68 °C (Prusament PETG) | Formech: good for low to medium forming temperatures, recommended |
| ABS | HDT 85 °C (Extrudr DuraPro ABS) | Formech: better suited than PLA, recommended |
| ASA | HDT 93 to 96 °C (Prusament, Extrudr) | Formech: similar to ABS, moderate heat |
| PC | 113 °C (Prusament PC Blend) | Formech: very good for heat-resistant tools, needs a high-temperature printer with enclosure |
| Nylon with carbon fibre | depending on grade | Formech: ideal for strong, long-lasting tools |
| TPU | depending on grade | Formech: unsuitable because it is not rigid |
The data sheet values and their meaning are covered in detail under UV-resistant and heat-resistant filament. Mayku generally advises a master material that only melts above the temperature of the sheet, ideally above 100 °C.
If you work with resin printing: according to Mayku, standard resin is only good for a single-use mould and crumbles with repeated use at around 70 °C. High-temperature resin withstands considerably more; Formlabs gives an HDT of 238 °C for its High Temp Resin. On the other hand, according to Mayku, resin delivers such smooth surfaces that no post-processing is needed, and Mayku therefore calls resin masters particularly suitable for chocolate moulds.
Walls and infill
A printed master has to withstand heat and negative pressure without collapsing. For PLA, Mayku expressly names a high infill. If a master has melted during forming, Mayku recommends reprinting it with thicker walls. For early prototypes, according to Mayku, the printed master can also be filled with plaster to make it more stable. How walls and fill work together is explained under Walls and top layers and Infill.
Between two runs the master should, according to Mayku, cool slowly. For moulds made of Grey Resin, Formlabs gives a cooling time of 8 to 10 minutes between two parts.
Draft angles
Vertical walls are hard to demould; the sheet jams on the master. All side faces therefore get a draft. The manufacturers’ figures differ:
- Mayku: at least 5°, for rigid sheets such as PETG and HIPS 8°, for flexible EVA sheet no draft needed.
- Formlabs: 4 to 5° for positive masters, 1.5 to 3° for negative ones, more for deep parts and textured surfaces.
- xTool: 3 to 5° draft and rounded edges.
The more rigid the sheet and the taller the master, the more draft.
No undercuts
Undercuts are places where the sheet reaches behind an edge, for example a step or a notch on the side. According to Mayku, you then cannot get the master out after cooling. Exceptions and ways out according to Mayku and Formlabs:
- Flexible sheet such as EVA tolerates small undercuts and even raised lettering on vertical walls.
- Multi-part master, whose parts can be removed one after another. Formlabs mentions magnets that hold the parts together.
- Cut line provided in the master, along which the part is later cut open.
Shape and spacing
- Wider than tall. According to Mayku, wide parts form more easily than tall ones. To avoid tears, Mayku advises not forming anything taller than it is wide.
- Recesses not too deep. For cavities, according to Mayku, the depth should be at most two thirds of the opening width. The sheet gets thinner as it stretches: if the area doubles, the thickness halves on average.
- Round the edges. According to Mayku, sharp angles below 90° lead to wrinkles and tears. In a Mayku article, the designer Agustín Arroyo writes that even a 2 mm radius makes a big difference.
- Spacing between several masters greater than the height of the tallest master, otherwise wrinkles form between them (Mayku).
Vent holes
Otherwise air stays trapped in recesses and corners, and the sheet only lies loosely there. Mayku counts FFF prints (that is, FDM) among the non-porous materials that need air holes. According to Mayku, porous SLS prints do not need any.
| Source | Hole size | Position |
|---|---|---|
| Mayku | 0.5 mm at the surface, widening inwards, larger for FDM if necessary | sparingly, in recesses near edges and corners |
| Formech | about 1 mm for sheets up to 2 mm, 1.5 mm for thicker ones, 0.75 mm or smaller for sheet under 1 mm | at the lowest point of recesses, at transitions, in every corner, about 25 mm apart |
| Formlabs | diameter matched to the sheet thickness | in internal recesses |
According to Mayku, holes that are too large can burst in thin sheet. With FDM, filament easily settles in very small holes, so check them before forming, for example with compressed air. Formech also recommends raising the master about 1 mm from the base board instead of drilling holes all round, for example with wire mesh, washers or thin strips. This gives a stronger airflow.
Smooth surface
The sheet reproduces every layer line. You can not only see this; according to Mayku it also makes demoulding harder. What helps:
- Fine layers. In the Mayku article, Agustín Arroyo recommends 0.1 mm layer height. More under Layer height.
- Sanding. Mayku advises sanding off the layer lines. Filler and sandpaper for large areas, sandblasting for fine details.
- Filling gaps. Mayku recommends wood filler because it adheres to the print and sands well. According to Mayku, plaster does not adhere to printed plastic and is more likely to stay stuck in the sheet.
- No supports on forming surfaces (Formlabs), otherwise marks remain.
How to sand and fill printed parts is explained under Post-processing 3D prints.
Release agent
For parts that do not come into contact with food, Mayku recommends PTFE spray in four coats on the master. For moulds into which edible material is cast, Mayku expressly advises against it. xTool mentions talcum powder or release spray if necessary. Formlabs mentions silicone release agent.
Sheet types
| Sheet | Typical thicknesses for desktop machines | Properties according to the manufacturer | Typical applications |
|---|---|---|---|
| PETG | 0.5 and 1.0 mm (Mayku, xTool) | strong, clear, easy to form, chemical-resistant. Mayku and xTool describe their PETG sheet as food-safe. | Packaging, transparent prototypes, casting moulds |
| PET (APET, RPET) | no manufacturer figure for desktop machines | clear, narrow temperature window, crystallises when overheated (Formech) | Blisters, tray inserts (Formech) |
| HIPS (polystyrene) | 0.5 mm (Mayku), 0.5 and 1.0 mm (xTool) | strong, inexpensive, easy to form, can be painted, cut and glued. More brittle than PETG, may get white stress marks when demoulded (xTool) | Packaging, housings, model making, figures, displays |
| ABS | 1.5 mm in the Formech and Formlabs test | more impact-resistant than HIPS, must be dried beforehand, 90 minutes per mm (Formech) | Housings, outdoor parts |
| PC (polycarbonate) | no manufacturer figure for desktop machines | stiff and very impact-resistant, must be dried, Mayku gives 90 to 120 °C for 6 to 12 hours. Forming temperature 170 to 205 °C (Formech) | Bodies for RC cars, protective screens |
| PVC | no manufacturer figure for desktop machines | easy to form, chemical-resistant. Releases hydrochloric acid when burned (Formech), Mayku advises against PVC | Blisters, tray inserts, outdoor housings |
| PP, PE | Formlabs test: PP 1.0 mm, PE 2.0 mm | robust and chemical-resistant, but according to Formech difficult: stretches a lot, wrinkles easily, finds every gap in the master | Packaging, robust parts |
| EVA | 1 mm (Mayku Flex Sheet) | flexible and tear-resistant, -35 to 60 °C, resistant to many casting materials such as resin, easy to demould (Mayku) | reusable casting moulds, moulds with small undercuts |
| TPU | 0.5 and 1.0 mm (xTool) | soft, rubbery, easiest to demould. xTool describes its TPU sheet as food-safe. | Casting moulds, dust and protective covers |
Two basic rules from the manufacturers’ figures:
- Thin or thick: Thin sheet heats up faster and reproduces finer details, but the finished part is softer or more brittle. Thick sheet is more stable but reproduces the finest details less sharply (xTool). Formlabs gives a rule of thumb: minimum sheet thickness equals draw ratio times desired final thickness, with a draw ratio of 3:1 considered the upper limit.
- Mind the machine’s limit: According to the manufacturer, the Mayku FormBox tolerates sheet no thicker than 1.5 mm. What your machine can handle is stated in its manual.
A sheet is food-safe only if its manufacturer states so. For sheets without a statement, do not assume it. The printed master itself does not touch the food, but the sheet does. More on the subject under Food-safe printing.
Nadin’s experience with the xTool WonderPress
Nadin tried vacuum forming with the 3D Form Module of the xTool WonderPress. The machine was provided to her by xTool as a beta tester. Of all the modules, vacuum forming had the steepest learning curve for her.
- Soft TPU sheet did not give her good shapes. With a suitable vacuum forming sheet, the shapes came out well.
- She formed a blister pack over a 3D-printed master.
- Her conclusion: “It depends heavily on the right sheet for the right purpose. A sheet that is too rigid does not work if you want to cast something that you want to get out again, for example wax. On the other hand, it is good for packaging. You cannot use the same sheet for everything.”
Which sheet for which purpose
| Purpose | Sheet according to the manufacturer | What to watch for |
|---|---|---|
| Casting mould for wax (candles) | xTool names PETG, TPU and HIPS, Mayku Clear Sheets (PETG) | Nadin: a sheet that is too rigid lets the wax out poorly. Mayku: keep the casting material below 50 °C, PETG sheet deforms from about 60 °C. Let the wax cool until a skin forms, then at around 50 °C put the mould in cold water. |
| Casting mould for soap | xTool names TPU, Mayku names soap as a suitable casting material | Temperature limit 50 °C as with wax (Mayku) |
| Casting mould for plaster | xTool names PETG, TPU and HIPS, Mayku Clear Sheets | Mayku: its own dental plaster Mayku Pour sets in just under 30 minutes and should then dry for at least 48 hours |
| Casting mould for concrete, Jesmonite | Mayku names both as casting material, but no specific sheet | no manufacturer figure on the sheet |
| Casting mould for chocolate | xTool names PETG and TPU, Mayku Clear Sheets (PETG) | only food-safe sheet, no PTFE spray. Mayku: tempered chocolate shrinks slightly as it cools, which helps it release. |
| Casting mould for resin | Mayku Resin Sheets (1.5 mm), Mayku Flex Sheets (EVA), xTool PETG and TPU | For resin, Mayku advises its Resin Sheets |
| Packaging, blisters | PETG (xTool, Mayku), PET and PVC (Formech), HIPS for opaque packaging | rigid sheet holds the shape. For food packaging, only sheet with a corresponding manufacturer statement. |
| Protective and dust covers | TPU (xTool), PETG for clear covers (Formech) | flexible sheet for parts that move or are meant to be removable |
| Model making, housings, figures | HIPS (xTool, Mayku), ABS (Formech), PC for very impact-resistant parts such as RC bodies (Formech) | According to Mayku, HIPS can be painted with primer and labelled with a pen |
If the casting material is hotter than the sheet can withstand, Mayku advises first casting a mould from silicone or plaster and processing the hot material in that. Mayku also warns: do not put Clear Sheets in the oven or microwave.
Common mistakes
| Mistake | Common cause | Solution |
|---|---|---|
| Wrinkles (webbing) | master too tall or too pointed, masters too close together, sheet too hot, frame lowered too quickly (Mayku) | round edges, more draft, master wider than tall, spacing greater than the height, lower the frame briskly but evenly |
| Sheet tears | sharp edges, recesses too deep, sheet too thin for the draw depth, vent holes too large (Mayku, Formlabs) | radii, recess at most two thirds of the width, thicker sheet, smaller holes |
| Sheet turns milky or white | overheated, the sheet crystallises (Mayku, for PET also Formech) | heat for less time, form as soon as the sheet sags |
| Bubbles in the sheet | moisture with ABS or PC (Formech, Mayku) | dry the sheet beforehand |
| Master is stuck | no or too little draft, undercuts, rough layer lines, sheet too rigid | more draft, remove undercuts, sand, release agent, more flexible sheet. Mayku: press in the middle on a soft surface or cut out just next to the part (under 10 mm). |
| Master deforms or melts | filament not heat-resistant enough, walls too thin, too many runs without a break | PETG, ABS, ASA or PC instead of PLA, thicker walls, more infill, let it cool between runs |
| Details missing, sheet only lies loosely | trapped air, sheet too cold or too thick | vent holes at deep spots and corners, blow the holes clear, raise the master slightly, thinner sheet |
| Layer lines in the result | sheet reproduces the print surface | finer layer height, sanding, filling, resin printing for smooth moulds |
Machines in the wiki
The technical data of the xTool WonderPress with its 3D Form Module are in the xTool WonderPress data sheet. How the press itself works is explained under Using a heat press correctly.
Sources
- Process, master material, draft angles, undercuts, vent holes, spacing, draw depth: Mayku Knowledge Base: Tool design and creation
- Sheet types PETG, HIPS, EVA, sheet thickness, drying PC, note on PVC: Mayku Knowledge Base: Understanding thermoformable materials
- Casting materials, 50 °C limit, wax, chocolate, plaster: Mayku Knowledge Base: Casting materials
- Melted master, wood filler, checking holes, durability: Mayku Knowledge Base: Tool troubleshooting
- Wrinkles, overheating, PTFE spray, demoulding, painting: Mayku Knowledge Base: Material troubleshooting
- PLA with high infill, standard and high-temperature resin: Mayku Knowledge Base: What 3D printers do you recommend?
- 0.1 mm layer height, 2 mm radius, surface: Mayku: How to Design for Vacuum Forming and Mold Making with Agustín Arroyo
- Sheet thicknesses, uses and food suitability of the Mayku sheets: Mayku: Clear Sheets and Mayku FormBox Materials TDS (PDF, September 2022)
- Filaments for vacuum forming tools: Formech: A Guide to 3D Printing Materials for Vacuum Forming (PDF, August 2025)
- Forming temperatures and properties of the sheets: Formech Technical Newsletter: Popular materials and applications
- Size and position of vent holes, raising the master: Formech Technical Newsletter: Vacuum and vacuum holes
- Process, drafts for positive and negative masters, draw ratio: Formlabs: Prototyping Packaging With Vacuum Forming and 3D Printed Molds
- Hollow masters, hole size by sheet thickness, undercuts with multi-part masters, release agent, cooling times, sheet thicknesses from tests: Formlabs: Thermoforming with 3D printed molds
- TPU, PETG and HIPS compared, sheet thicknesses, casting materials, demoulding: xTool Support: TPU vs. PETG vs. HIPS: Which Vacuum Forming Film Should You Use?
- Heat deflection temperature of the filaments: see the sources under UV-resistant and heat-resistant filament
- Nadin’s experience: her own test of the xTool WonderPress (video “xTool WonderPress im Komplett-Test: Alle Module ausprobiert, lohnt sie sich?”)