Ask what makes a clear aligner comfortable, invisible and effective, and the answer usually comes down to one thing: the material. The tray is only as good as the film it's thermoformed from. So what are clear aligners made of, and why has medical-grade multilayer PETG become the default across serious aligner manufacturing?
Key takeaways
- Most quality clear aligners are thermoformed from medical-grade PETG (polyethylene terephthalate glycol).
- Multilayer films retain corrective force longer than single-layer plastics — steadier, gentler movement.
- Biocompatibility testing to ISO 10993 is non-negotiable for anything worn in the mouth all day.
- Clarity, thickness and force retention are the numbers worth checking on any spec sheet.
What is PETG?
PETG stands for polyethylene terephthalate glycol — a glycol-modified version of PET, the same family of plastic used in food-safe packaging. The glycol modification makes it tougher, clearer and easier to thermoform without going brittle. In aligner manufacturing, PETG is supplied as thin sheets that are heated and pressure-formed over a printed model of the patient's teeth.
Why PETG dominates clear aligner manufacturing
Optical clarity
The whole point of a clear aligner is that people don't notice it. Good PETG film transmits more than 90% of visible light, so the tray stays genuinely transparent on the teeth rather than cloudy or grey.
Force retention
An aligner works by holding a small, sustained force that nudges a tooth toward its planned position. Single-layer plastics tend to relax quickly, losing much of that force within hours. Multilayer PETG — layers with different mechanical roles laminated together — holds force more steadily across the wear period, which means gentler, more predictable movement.
Comfort and fit
PETG forms tightly and trims to a smooth edge, so a well-finished tray seats cleanly along the gumline without sharp spots. Comfort drives compliance — a tray that's comfortable is a tray the patient actually keeps in.
Biocompatibility
Anything worn against oral tissue for most of the day must be safe. Reputable aligner films are biocompatibility-tested to ISO 10993 and are BPA-conscious, giving clinics and patients confidence in what's in the mouth.
What to check on a material spec sheet
- Grade: is it medical-grade, and biocompatibility-tested to ISO 10993?
- Construction: single-layer or multilayer? Multilayer for better force retention.
- Formed thickness: commonly around 0.75 mm after forming — enough to hold force, thin enough to stay comfortable.
- Optical clarity: light transmission above ~90% keeps the tray invisible.
- Stain and wear resistance: the tray should stay clear across its wear cycle.
A perfect treatment plan formed in the wrong plastic still fails the patient. Material is where comfort and results are decided.
Material is only half the story
Even the best film underperforms if it's formed over an inaccurate model or trimmed carelessly. Material quality and manufacturing quality work together — which is why it's worth understanding the full manufacturing process and how to vet a manufacturer before committing your cases.
Aligners engineered around the material
AlignoDontic thermoforms medical-grade multilayer PETG and checks clarity, edge and fit on every tray before dispatch.