PETG sheet thickness tolerance is where a specification quietly changes the process window. A packaging converter ordered 3 mm PETG for a tray that had passed every prototype test. Production trays failed a drop test at the corners. The sheet met the supplier specification at 2.82 mm. The prototype had been formed from 3.05 mm. That 0.23 mm difference, multiplied by the draw ratio, was the whole failure.
PETG sheet thickness tolerance is a commercial term that buyers read as a quality term. Both statements are true; the problem is that the two rarely mean the same number.
PETG sheet thickness tolerance by gauge
- 0.5 mm to 1.5 mm: about plus or minus 10 percent, thin-gauge extrusion
- 2 mm to 4 mm: plus or minus 8 to 10 percent as standard, 5 percent by agreement
- 5 mm to 8 mm: plus or minus 5 percent achievable on a controlled line
- Above 8 mm: usually machined or polished to a finished size, not extruded to it
Ask a supplier whether the tolerance is applied to nominal or minimum. A 3 mm sheet at plus or minus 10 percent of nominal can legitimately arrive at 2.70 mm. If your forming process needs 2.9 mm minimum, the order has to state that as a minimum, and the price will move.
Measurement method matters as much as the number. Calipers on a cold sheet, five points, 25 mm in from the edge, averaged. A micrometer on a warm sheet reads low because the material is still soft from the line.
How tolerance shows up downstream
In thermoforming, wall thinning is the mechanism. A 3 mm sheet drawn into a 150 mm deep tray will thin to roughly 2 mm at the base corners. Starting from the low end of tolerance, the same draw lands at 1.75 mm, and the corner is where a drop test finds it.
In pricing, tolerance is a hidden cost. A sheet that runs consistently at the top of tolerance gives more square metres per tonne, which is why some suppliers quote cheaper and ship heavier. Compare price per sheet only after confirming the measured gauge, not the callout.
In fabrication, thickness variation changes the cut setting. A CNC router programmed for 3.00 mm will leave a burr on a 2.85 mm sheet. Buyers who cut PETG in volume usually specify a narrow tolerance band and pay for it, because the scrap rate falls more than the price rises.
For the standards behind the callouts, the standard sizes and thickness guide covers how sheet formats are quoted in this industry, and our PETG cut-to-size service guide explains how a finished part is specified instead of a raw sheet.
If the tray will carry food, the gauge question sits alongside the compliance question, which the PETG FDA compliance guide covers.
Ask for a measured thickness report with your order at oversales@rpplexiglass.com.
Frequently Asked Questions
What is the normal thickness tolerance for PETG sheet?
Extruded PETG typically runs within about plus or minus 10 percent on thin gauges, tightening to plus or minus 5 percent on heavier sheet by agreement. Always confirm whether the figure is a nominal or a minimum.
Where should thickness be measured?
At five points: each corner and the centre, at least 25 mm in from the edge. Measuring only the middle of a sheet gives a flattering number, because extruded sheet is usually slightly thicker at the centre line.
Why does thickness matter for thermoforming?
Because the draw thins the wall. A 3 mm sheet at the bottom of tolerance becomes 2.4 mm after a deep draw, and the part fails a strength check that the design assumed would pass.