Prohibited Materials for Laser Cutting: What You Must Never Laser
are explained briefly when you hover over or tap them.
Not everything a laser can cut is something it should cut. Some plastics form corrosive or toxic gases when lasered, others catch fire quickly or melt into burning drops. This overview shows which materials are prohibited, why, and how to identify unknown ones.
The overview
| Material | Typically found in | Problem | Classification |
|---|---|---|---|
| PVC (rigid and flexible) | Pipes, foam boards, films, cable insulation | Hydrogen chloride, which turns into hydrochloric acid with moisture; chlorine gases; corrosion of the machine and optics | prohibited |
| Vinyl | Plotter film, vinyl records, flooring | Mostly PVC, same gases | prohibited |
| Synthetic leather with PVC | Bags, upholstery, labels | PVC coating on fabric | prohibited |
| Polycarbonate (PC, Lexan, Makrolon) | Protective screens, housings, phone cases | Discolours, melts, can ignite, lots of smoke | prohibited for cutting |
| ABS | Housings, toys, 3D-printed parts | Melts instead of vaporising, can burn, harmful fumes | prohibited |
| HDPE | Milk bottles, plastic chopping boards | Melts and burns, sticky residue | prohibited |
| PTFE (Teflon) | Seals, sliding films, coatings | Fluoroplastic, dangerous gases when heated | prohibited |
| Fibreglass (GRP) | Circuit boards, boat building, sheets | Glass cannot be cut, resin forms fumes, fine dust | prohibited |
| Carbon (CFRP), coated | Frames, sheets, trim parts | Resin and fibres, conductive fine dust on electronics and optics | prohibited |
| Polystyrene foam (Styrofoam) | Packaging, insulation | Ignites very easily, melts | prohibited |
| PP foam | Packaging, cushioning | Burning, dripping melt | prohibited |
| Galvanised steel, zinc sheet | Sheets, perforated sheets, magnetic boards, gutters | Zinc oxide fumes, can trigger metal fume fever | only with a fibre laser, enclosure and extraction, see Laser cutting metal |
| Coated materials of unknown type | Painted boards, foil-covered wood, synthetic surfaces | Unknown gases, often PVC film or halogen-containing paints | only with a datasheet |
| Unknown plastics and recycled boards | Offcuts, mixed plastics | Unknown composition, flame retardants | only with a datasheet |
The list is based on manufacturers’ material lists (Thunder Laser, FLUX) and the widespread “Never cut list” from makerspaces. It is not exhaustive. If in doubt, the rule is: do not laser it.
Why PVC is so dangerous
PVC contains chlorine. When heated, hydrogen chloride is produced. Together with moisture in the air, in your airways and on metal surfaces, it forms hydrochloric acid. This has two consequences:
- For you: Irritation of the eyes, skin and lungs. The fumes are considered harmful to health and in part carcinogenic.
- For the machine: Guides, screws, mirrors and electronics corrode. Even a few jobs can leave damage that only shows weeks later.
Extraction does not change this. The gases are produced directly at the laser spot and attack everything in the machine before they are extracted.
Synthetic leather also often contains PVC, not only as the main material but as a coating on a fabric. Many names such as “imitation leather”, “Skai” or “vegan leather” say nothing about the material. PU synthetic leather is usually less problematic but still needs a datasheet. Real leather is a topic of its own, see Laser cutting leather.
Confusing polycarbonate and acrylic
Polycarbonate and acrylic (PMMA) look almost the same. Acrylic can be cut superbly with a CO₂ laser, polycarbonate cannot. It turns yellow to brown, melts at the edges, produces a lot of smoke and can ignite.
Here is how to tell the two apart without a laser:
- Bending: Polycarbonate bends a long way before it breaks. Acrylic breaks in a brittle way.
- Edges: Cast acrylic often has a clear, slightly bluish edge.
- Marking: Protective films often say PC, PMMA, Plexiglas or Makrolon.
- Origin: Protective screens, visors and shatterproof parts are almost always PC.
More on the difference and on suitable types of acrylic in the article Laser cutting acrylic.
Melting plastics: ABS, HDPE, foams
ABS, HDPE, polystyrene foam and PP foam do not vaporise cleanly. They melt, form viscous drops and catch fire easily. The drops partly keep burning even when the laser has already moved on. In makerspaces, Styrofoam is considered the most common cause of laser fires.
The problem mainly affects cutting with diode and CO₂ lasers. Some manufacturers of UV or infrared machines list ABS as a material for surface marking. That is a different process with very little heat. Rely only on the material list of your own machine for this.
Composites: fibreglass and carbon
With GRP and CFRP you run into two problems at once. The resin forms fumes, and the fibres leave fine dust. Carbon dust is electrically conductive and can settle on circuit boards. A hobby laser cannot cut glass fibres anyway, it only burns the resin around them.
Coated and unknown materials
Most accidents do not happen with obvious PVC but with materials that nobody looks at closely:
- foil-covered plywood or furniture boards with a plastic surface
- painted sheets with an unknown paint
- plastic signs from the DIY store with no information
- packaging, foams and offcuts from the workshop
Only one rule helps here: Without a datasheet or clear manufacturer information, do not laser it. You can get laser-suitable materials from specialist retailers who state the plastic.
Identifying a material
If you cannot place a piece:
- Look for the recycling code. The number in the triangle reveals the plastic: 3 is PVC, 2 is HDPE, 5 is PP, 6 is PS. The codes 1 to 7 are standardised, and 7 means “other” and does not help.
- Ask for a datasheet. Reputable retailers name the plastic.
- If in doubt, leave it out. A corroded machine or irritated lungs are not worth the material you saved.
The burn test with copper wire (Beilstein test) is sometimes recommended for detecting chlorine. But it produces exactly the gases you want to avoid. For hobby use, the route via datasheet and marking is safer.
If it has happened anyway
- Stop the laser immediately, keep the extraction running.
- Ventilate the room well and leave the room yourself.
- After cooling, clean the machine: check guides, mirrors and lens for deposits, wipe metal parts.
- If you have difficulty breathing, seek medical advice.
Continue with: Laser safety and Extraction when lasering.