Polycarbonate cold bending is the shortcut that works until the panel decides it does not want to stay curved, and the difference between a good result and a cracked sheet is one ratio.
A signage fabricator bent 8 mm panels to a 500 mm radius for a station canopy. The panels looked right at install and two cracked along the bend line in the first summer, because the radius sat under the limit and the frame was unyielding.
Polycarbonate cold bending radius and thickness
- Permanent curve: radius 100 times thickness
- Temporary install: radius 50 times thickness
- Span: bend over the full width, not in a corner
- Frame: curved to match, gasketed, not straight
The ratio is a stress limit, not a manufacturing opinion. At 100 times thickness the outer fibre stress stays in a range the sheet tolerates for years; at 50 times it tolerates months.
Spring-back, heat and the frame
Spring-back is predictable. A cold bent panel recovers a fraction of its curvature once released, so the bending frame is built slightly tighter than the finished radius, and the panel is installed before it relaxes.
Heat is the multiplier. A curved panel at 40 C expands against a rigid frame and the bend line takes the load; a frame with 2 to 3 mm of clearance and a compliant gasket absorbs the movement.
For where the cut panel comes from, polycarbonate cut to size covers the blank preparation.
Send your radius, panel size and service temperature to oversales@rpplexiglass.com for a bending assessment.
Frequently Asked Questions
What is the minimum cold bend radius for polycarbonate?
About 100 times the sheet thickness for a permanent curve, 50 times for a temporary installation. A 6 mm panel needs roughly a 600 mm radius to hold a curve without stress crazing.
Why does a cold bent panel spring back?
Elastic recovery. Polycarbonate bent cold stores energy in the sheet; without a frame holding the curve it recovers 10 to 20 percent of the deflection over the first weeks.
Can cold bent polycarbonate be used outdoors?
Yes if the curve is gentle and the panel is restrained. Thermal expansion on a curved outdoor panel pushes against the frame; a radius near the limit plus a hot day is the combination that cracks.