Vacuum Forming Guide: How It Works, Which Plastics to Use, and What Size Machine You Need

Quick answer: Vacuum forming heats a plastic sheet until it sags, then pulls it tight over a mold with suction so it takes the mold's shape. A desktop machine can make packaging trays, cosplay armor, molds for soap and chocolate, signage and product prototypes in minutes per part. The two numbers that decide which machine you need are forming area (how big a footprint you can form) and draw depth (how tall a mold you can form over). The MYYARD lineup we carry runs from the compact FORMART S (about 12 x 8 inch area) to the FORMART SE and FORMART 2 (about 18.5 x 10.6 inch area) and the production-focused FORMART 3. All four offer a 160 mm (6.3 inch) maximum draw height. You can compare them side by side in our vacuum formers collection.

Table of Contents

• How Vacuum Forming Works
• Vacuum Forming vs Pressure Forming vs Injection Molding
• Which Plastics to Use
• How to Make Molds That Release Cleanly
• What Size Vacuum Former Do You Need?
• What People Actually Make
• Troubleshooting Webbing, Thinning and Poor Detail
• Which FORMART Is Right for You?
• Frequently Asked Questions

How Vacuum Forming Works

Vacuum forming is the simplest type of thermoforming, and every desktop machine follows the same five-step cycle.

1. Clamp the sheet. A plastic sheet is locked in a frame above the forming bed so air cannot leak around the edges.
2. Heat until it sags. Heaters above the sheet bring it to its forming temperature. The visual cue is a gentle, even sag in the middle of the sheet.
3. Bring the sheet and mold together. The softened sheet is lowered over the mold (or the bed rises into it), so the plastic drapes over the shape.
4. Pull the vacuum. A pump evacuates the air between sheet and mold through the perforated bed, and atmospheric pressure pushes the plastic tight against every surface.
5. Cool, release and trim. Once the plastic cools below its softening point, the part keeps its shape. You pull the mold out and trim the excess flange with a knife, scissors, a laser or a CNC.

Modern desktop machines automate most of this. The FORMART lineup uses quartz heaters with a 140–446°F range and built-in vacuum pumps, and the FORMART 3 adds 16 material presets that load the heating curve, vacuum mode and timing for you, plus a 300W pump rated to -92 kPa.

Vacuum Forming vs Pressure Forming vs Injection Molding

Vacuum forming's advantage is cheap, fast tooling. You can print a mold overnight and pull your first part the next morning, which is why it sits so naturally alongside 3D printers, CNC routers and lasers in a maker shop.

Which Plastics to Use

Desktop vacuum formers handle thermoplastic sheets, typically from 0.3 mm up to 3 mm thick on the FORMART lineup. Thinner sheet captures detail more easily. Thicker sheet makes stronger, more rigid parts but needs more heat and a stronger vacuum.

We stock MYYARD sheet stock sized for the FORMART machines, including white HIPS, transparent PET, LDPE and TPU. Buying sheets cut to your machine's frame size removes the most common source of air leaks.

How to Make Molds That Release Cleanly

Most vacuum forming failures are really mold design failures. A good mold can come from almost anything that survives the heat and the suction.

What to make molds from

• 3D prints. The most popular option. PLA softens at fairly low temperatures, so print in PETG or ABS for molds you will reuse, or use a high infill so PLA does not deform under heat and vacuum.
• CNC-machined wood or MDF. Durable and smooth once sealed. A CNC router is ideal for large, shallow molds like signage letters and trays. Our guide on CNC routers vs laser cutters covers when a router earns its place.
• Laser-cut stacked layers. Stack laser-cut MDF or acrylic layers for stepped or terraced shapes, then sand smooth.
• Found objects and clay. Real fruit, figurines and air-dry clay all work for one-off molds, as long as they can take the heat.

Design rules that prevent stuck parts

• Add draft. Give vertical walls a 3–5 degree taper so the part slides off. Perfectly vertical walls grip the mold.
• Avoid undercuts. Any overhang locks the plastic onto the mold. Split complex shapes into multiple molds instead.
• Round the corners. Sharp internal corners thin the plastic and can tear it.
• Drill vent holes in deep recesses. Small holes (about 1 mm) in cavities let trapped air escape so the plastic reaches the bottom.
• Raise the mold slightly. Setting the mold on a thin riser makes the trim line cleaner and the part easier to pull.

If you sell 3D-printed or formed products, our guide to UV printing on 3D-printed parts shows how makers add full-color branding to finished pieces.

What Size Vacuum Former Do You Need?

This is the question that decides your budget, and it is where most buyers guess wrong. Based on the calls our team fields every week, people usually size the machine to the part, not to the part plus the clearance the plastic needs to wrap around it.

Rule 1: Footprint plus margin

The plastic needs room to drape down the sides of the mold and seal against the bed. Plan for at least 1 to 2 inches of clear space on every side of your mold, and more for tall molds. A 10 x 6 inch part sits comfortably on a 12 x 8 inch machine only if it is shallow.

Rule 2: Height is limited by stretch, not just by draw height

All four FORMART models list a 160 mm (6.3 inch) maximum draw height. In practice, the deeper you pull, the thinner the walls get, because a fixed amount of sheet stretches over more surface. A useful rule of thumb for a single mold is to keep its height at or below about half of its narrowest width if you want reasonable wall thickness without plug-assist tooling.

Rule 3: Batch size changes the math

If you plan to form several small parts per cycle (soap molds, packaging inserts, keychain blisters), the bigger forming area pays for itself in cycle time. If you mostly form one item at a time, a compact machine wastes less plastic per part.

The FORMART 3's four switchable frame sizes are its quiet advantage for small businesses. You can run small sheets for single parts and large sheets for batches without wasting plastic on an oversized border.

What People Actually Make

• Packaging and retail displays: blister packs, clamshells, product trays and inserts for small-batch brands.
• Cosplay and props: armor plates, helmets made in sections, masks and replica parts, usually in HIPS or ABS.
• Molds for casting: trays for soap, candles, chocolate, resin and concrete. Use food-contact rated sheet for anything edible.
• Signage: raised letters and logos formed over CNC-cut or laser-cut shapes.
• Product prototyping: enclosures and covers to test fit and feel before paying for injection molds.
• Education: design and technology classrooms use desktop formers to teach manufacturing in a single lesson.

Based on our experience selling equipment to universities, schools and businesses of all sizes, vacuum formers are most valuable in shops that already have a 3D printer, laser or CNC. Those tools make the molds, and the former turns them into repeatable parts.

Troubleshooting Webbing, Thinning and Poor Detail

Which FORMART Is Right for You?

Choose the FORMART S if you are learning, forming one small part at a time, or buying for a home studio or classroom where 12 x 8 inch sheets cover the work.

Choose the FORMART SE or FORMART 2 if you need the larger 18.5 x 10.6 inch forming area for cosplay pieces, signage or batches of small parts. Compare the two product pages for the feature differences that matter to your workflow.

Choose the FORMART 3 if you run a small business or production workflow and want presets, a stronger 300W pump and four frame sizes that cut plastic waste between small and large jobs.

Based on the feedback from real Maker's Chest customers, buyers who are unsure between sizes are rarely sorry they went larger, because the larger frame still forms small parts while a small frame can never form large ones.

Frequently Asked Questions

What is the best plastic for vacuum forming beginners?

HIPS (high-impact polystyrene) is the easiest plastic to learn on. It forms at a forgiving temperature, captures detail well, and is cheap enough to practice with. Move to PETG or PET when you need clear parts.

Can you vacuum form over a 3D print?

Yes. 3D-printed molds are the most common choice for desktop vacuum forming. Print in PETG or ABS for reusable molds, use high infill, add a 3–5 degree draft and avoid undercuts.

How deep can a desktop vacuum former pull?

The FORMART lineup lists a maximum draw height of 160 mm (6.3 inches). Deeper pulls thin the walls, so keep tall molds no higher than roughly half their narrowest width for strong parts.

What size vacuum forming machine do I need?

Measure your largest part, then add at least 1 to 2 inches of clearance on every side. If that fits within 12 x 8 inches, a compact machine works. If not, or if you want to form batches, choose a machine with an 18 x 10 inch class forming area.

Is vacuum forming food safe?

It can be if you use plastic sheet that is rated for food contact, such as food-grade PET, and keep molds and equipment clean. Check the sheet supplier's food-contact certification before making anything edible.

What causes webbing in vacuum forming?

Webbing happens when excess plastic folds over itself, usually at corners or between molds placed too close together. Space molds further apart, reduce the frame size, lower the heat slightly or raise the mold on a riser.

What is the difference between vacuum forming and thermoforming?

Thermoforming is the umbrella term for shaping heated plastic sheet. Vacuum forming is the most common type and uses suction alone, while pressure forming adds compressed air for sharper detail.

Not sure which machine fits your parts? Contact our team with your part sizes and materials, and we will help you choose the right vacuum former and sheet stock.

Forming for a business?

MYYARD FORMART 3 Vacuum Forming Machine

A desktop vacuum former with a 300W pump, 16 material presets and four switchable frame sizes.

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Written By

Alina Oprea

Maker & Equipment Specialist

Alina Oprea is a hands-on maker, jeweler, and workshop specialist at The Maker’s Chest, with 25 years of silversmithing experience alongside a background in woodworking, renovations, construction, and commercial ductwork installation.

Her experience spans decorative woodwork, hand-carved doors, jewelry fabrication, homebuilding with Habitat, and real jobsite problem-solving — giving her a practical understanding of materials, tools, workflow, and what machines need to deliver beyond the spec sheet.