Short answer: To bend acrylic, heat a narrow strip along the bend line with a strip heater until the sheet is soft and rubbery, roughly 290 to 350 °F (145 to 175 °C) depending on the grade, then fold it in a jig and hold it until it cools. Heat sheet thicker than about 3/16 in. from both sides, keep the inside radius at least twice the sheet thickness, and don't let the surface pass about 410 °F or it will bubble.

How do you bend acrylic with a strip heater?

Most acrylic bends (stands, brochure holders, phone stands, sneeze guards with a foot) are line bends: a straight fold along one line. The tool is a strip heater, a long element under a narrow slot, so only a strip along the bend line gets hot.

Key facts

  • Forming temperature (sheet): Plexiglas G 290 to 360 °F; Röhm cast GS 320 to 347 °F (160 to 175 °C); extruded XT 302 to 320 °F (150 to 160 °C); Acrylite cast 340 to 380 °F; Acrylite extruded about 300 °F.
  • Strip heater setup (Plexiglas manual): element about 800 °F, not glowing red; sheet about 1/4 in. above it; sheet surface above 410 °F starts to bubble.
  • Heating time (Plexiglas, extruded): 1/8 in. about 2 1/2 minutes from one side; 3/16 in. about 3 minutes, flipping every minute; 1/4 in. about 4 minutes, flipping or heated from both sides.
  • Radius: Röhm says the bend radius should be at least twice the sheet thickness; tighter bends crease and hold stress.
  • Heated zone: 3 to 5 times the sheet thickness wide (Röhm).
  • Length: bends longer than about 24 in. tend to bow (Plexiglas, Plaskolite).
  1. Mark the bend line on the film with a fine marker, then peel the film from the heated area only.
  2. Lay the line over the heater without touching it; direct contact ruins the surface.
  3. For thick sheet, heat both sides. At 1/8 in., one side is usually enough. At 3/16 in. and up, flip every minute or use a two-sided heater so the core softens too; otherwise the inside of the bend is stressed.
  4. Test for softness. It should flex easily along the line with no resistance. If you have to force it, it isn't ready.
  5. Fold with the heated side on the outside of the bend, and set it in a jig at the angle you want.
  6. Hold it until it cools, typically one to several minutes. Moving it early lets it relax and change angle.

What temperature does acrylic bend at?

Acrylic starts to soften near its heat deflection temperature, about 195 to 210 °F (91 to 99 °C), but it bends cleanly only at forming temperature: roughly 290 to 350 °F for most sheet, with cast running a little hotter than extruded. Below that, the bend holds stress and may show white marks or crack later; Plexiglas warns that forming below about 275 °F leaves stresses that annealing can't fully remove. Well above it, the surface bubbles or scorches. Check your sheet maker's forming guide for exact numbers.

Why does acrylic bubble when I bend it?

  • Overheating. The most common cause. The surface gets far hotter than the core while you wait. Plexiglas says a glowing red element (about 1,500 °F) left just 15 seconds too long makes bubbling very likely. Lower the heat and take longer, or flip more often.
  • Moisture. Acrylic absorbs a little water. Heated hard, it turns into tiny bubbles inside the sheet, worst in extruded sheet and at the edges of stored stacks. Röhm says pre-drying normally isn't needed for line bending, but damp sheet bent hot can blister (see thermoforming acrylic for drying).
  • Heating too close. A heat gun or element held too near the surface blisters it before the inside warms up.

How do you get the angle right?

A jig can be as simple as two boards screwed together at the right angle. Acrylic springs back slightly as it cools, often a few degrees, so many people set the jig a little past the target angle and adjust after a test piece. Röhm explains the direction: the angle moves toward whichever face stays warm longest, so cover the bend with cloth or foam to cool both faces evenly.

The inside of a line bend ends up with a radius of at least about twice the sheet thickness. For a crisp outside corner, fabricators cut a 90° V-groove along the inside of the bend line before heating, but it weakens the part. More in minimum bend radius.

Can you bend near holes and edges?

  • Keep holes and cutouts at least a couple of sheet thicknesses away from the heated zone, or they'll distort into ovals.
  • If a hole has to sit close to the bend, drill it after bending.
  • The heated strip shrinks and thickens slightly. On small parts, edges near the bend can pull in a little; allow for it on tight fits.
  • Strip-heated bends hold stress. Keep cleaners, solvents, and cement off the bend, and anneal the part if it will be glued.

Is cast or extruded acrylic better for bending?

Both bend. Extruded acrylic softens at a lower temperature and heats faster, but it shrinks along its extrusion direction when heated (Röhm lists up to 3 to 6% for XT, versus a maximum of 2% for cast GS) and is more prone to moisture bubbles. Cast acrylic has a wider working range and is more forgiving, which is why it's usually preferred for display work. Cast vs extruded acrylic.

What about ovens and heat guns?

For curves and shapes that aren't a straight fold, heat the whole sheet in an oven and drape it over a form; see can you thermoform acrylic. A heat gun works for small, thin bends but heats unevenly; read can you heat gun acrylic before trying it. Boiling water won't do it: Plexiglas notes hot water and steam can't get acrylic to forming temperature.

Caution: Hot acrylic burns skin, and overheated acrylic gives off methyl methacrylate vapor. Use gloves, work with ventilation, and never leave a heater on unattended.

Let us bend it

We line-bend acrylic up to 1/4 in. thick, with the angle set by jig so every part matches. Add bends to your part in the instant quote or see acrylic bending.

Questions

Can you bend acrylic without heat?

Only into a gentle curve held in a frame, with a radius of at least about 180 to 330 times the thickness depending on the maker. Röhm states plainly that cold line-bending isn't possible with acrylic. See minimum bend radius.

Why did my bend turn white?

A white line at the bend means the acrylic was stretched while too cool, or the heated zone was too narrow. Heat it longer, from both sides if it's thicker than 1/8 in., until it folds with no resistance.

Can I re-bend acrylic if I get the angle wrong?

Usually, yes. Acrylic has elastic memory: reheat the same line and it relaxes back toward flat, then you can bend it again. Each reheat risks bubbles, so don't overdo it.

How thick can acrylic be and still be line-bent?

With heaters on both sides, quite thick: Röhm says quartz heaters can line-heat blocks over 2 in. (50 mm). Thick bends need wide radii and long, even heating, so most shop line bending stays at 1/4 in. and under.

Sources