Resin Print Stuck to the Film Instead of the Plate

Likely causes, most common first

1. Platform not calibrated, or calibrated wrongMost common
   Prusa says the most common cause of an object stuck to the bottom of the tank is an incorrect Z offset of the platform, and that recalibration can be needed even if nothing has changed. Formlabs lists too much space between the platform and the film or elastic layer.
2. Platform or its mount looseCommon
   A platform that is not locked down cannot reach the right position. Prusa says to tighten the knob on the platform after reinstalling it; Formlabs describes tightening the platform mount in half-turn steps and replacing the mount if the looseness returns.
3. Footprint too small, or too largeCommon
   Formlabs notes the first layer may be too small to resist the peel forces. At the other end, Prusa says models with a large footprint are prone to sticking to the film, especially when printed too fast, and suggests a different orientation.
4. Too few supports, or no raft or padCommon
   After every layer the printer peels the cured layer off the film. Prusa warns that a single support holding much of the object may not resist that force. Formlabs says a raft helps parts adhere to the platform.
5. Cloudy, dirty or damaged filmOccasional
   Prusa says a cloudy, dirty or damaged film hurts print quality and can block UV light so the resin does not cure. Formlabs says debris in the tank can block the light and stop the resin above it from curing.
6. Slicer profile not right for the resinOccasional
   Prusa recommends its tested resin profiles and notes that the first layers need much longer exposure than regular layers. The values come from the resin and printer profile, not from a universal number. See the resin exposure test.
7. Resin contaminated with alcoholLess common
   Prusa warns that isopropyl alcohol, for example from cleaning the platform, changes the resin's properties so it may not solidify.
8. Very sticky resin typeLess common
   Prusa notes that some resins, such as flexible resins, adhere strongly to both the platform and the film, and suggests its slower print profile.

Fix it, one change at a time

1. Stop the print as soon as you see an empty plate. Prusa says to stop immediately to avoid damaging the film.
2. Empty and clear the vat, wearing gloves and eye protection. Remove the vat, pour the resin through a filter into a separate bottle (Prusa: never back into unused resin), wipe the film until the cured patch is visible, then lift the patch with your fingertips, starting at an edge and working around. Prusa says not to use fingernails, and that the supplied plastic spatula can help. Check for small leftover fragments before the next print.
3. Clean and inspect the film. Use the cleaning method your printer maker gives for the film. Prusa says warm water with a little dish soap and soft paper towels, and never IPA or acetone on its film. Hold it up to the light: it should be clear, with no scratches, dents or holes.
4. Make sure the platform is locked and the vat is seated. Tighten the platform as your maker describes, and check that the vat sits flat.
5. Re-run the platform calibration from the maker's instructions, step by step. Prusa warns not to skip any step.
6. Print the sample file. If it succeeds, move on to your own file.
7. Re-slice your model with the maker's default profile for your resin. Orient it so the footprint suits the peel force, add a raft or pad, and add supports or raise support density where the model has a large area hanging on a few supports. See Resin Orientation and Supports.
8. Replace the resin if alcohol may have got into it, after cleaning and fully drying the vat.

Confirm it is fixed

The sample file and then your own file come out on the platform with every part present, and the emptied vat shows no cured patch on the film. Inspect the film again before the next print.

Why it happens

Every resin layer is cured in a thin gap between the last layer and the film at the bottom of the vat. The new layer bonds to both. The printer then pulls the platform up or tilts the vat so the layer peels off the film and stays with the part. The first layers have to win that tug of war against the film, so they need a firm, correctly spaced start on the platform.

If the platform sits too high, the first layer is cured in a gap that is too thick, or not fully against the platform, and the film wins. If the platform is loose, it cannot hold the right position. If the footprint is tiny, there is too little area to hold on. If the footprint is very large, the suction and peel force on the film are large too, which is why Prusa suggests reorienting and slowing down. A cloudy or dirty film works differently: it blocks some of the light, so the layer under the dirt does not cure enough to bond to anything.

A failed first layer also leaves a hazard behind: a cured slab on the film. If the next print starts on top of it, the platform presses down onto a hard object. Prusa warns that leftover cured pieces such as supports or pads can damage the tank bottom or the display, and its procedure starts with draining the vat and checking for even small fragments before the next print.

Handle all of this with gloves on. Liquid resin on the film, the platform and the failed patch is uncured, and the SDS classes typical resins as skin sensitizers and, depending on the resin, as eye irritants or a cause of serious eye damage. See Resin PPE and Resin Vat and Film Care.