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Hollow STL for Resin Printing

Hollow a model for resin printing in one step: set the wall thickness, and get a shell with drain holes at the lowest points of every cavity, matching plugs, and a report of the resin you save. Check the wall in a section view before you download.

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Drop an STL here or click to browse
Closed models work best · open meshes are repaired first · up to 150 MB
Choose STL
1
Upload STL
2
Wall and holes
3
Check and download
Holes per cavity
Two holes let air in while resin drains out, so the print does not act as a suction cup. Small cavities get one.
Bottom of the model
Holes go at the lowest points on this side (usually the base, −Z), where they drain best and are least visible.
Server-sideProcessed on our server, then deleted

Your file is uploaded to our server to be processed, so it does leave your device. Temporary files are removed as soon as processing finishes, and the uploaded original is deleted automatically within 120 minutes at the latest. Nothing is stored permanently.

About

A solid resin print is mostly resin you did not need. Hollowing keeps an outer wall and empties the inside: on a typical bust or statue that is 60 to 80 percent less resin, a lighter print and less suction on the FEP while it prints. This tool does the whole job on the server in one step. Upload an STL, choose the wall thickness, and you get a shell with drain holes already cut, a plug for each hole and a report of the resin saved, in seconds even for a million-triangle sculpt.

The wall is built the way slicers build it, from a distance field rather than by pushing vertices along their normals, so it does not fold into itself on ears, fingers or hair. Every point of the inner surface keeps at least the wall you asked for; parts thinner than two walls, such as limbs, swords or thin bases, simply stay solid, and the report tells you what share of the surface that is. Tiny pockets that could never drain are left filled instead of becoming resin traps.

Drain holes are the part most hollowing tools leave to you. Here every separate cavity gets its own: the first at its lowest point towards the base of the model, the second far enough from it to let air in while resin runs out, both drilled straight through the wall as Prusa recommends. Formlabs advises at least two holes and one near the build platform; the default does exactly that. You can choose the hole size and count, flip which side is the base, or click on the model in the preview to put holes where you want them and run it again.

Before anything is offered the result is checked: it must be a closed, manifold solid, every cavity must open to the outside through a hole, and the wall is measured back from the result. A model that is not closed is repaired first; if it still cannot be closed, or nothing is thick enough to hollow, you get a message and are not charged. The section view lets you slide a plane through the part and see the wall. One hollowing a day is free; a credit pack, a 24-hour pass or a subscription covers more, shared with the other 3D tools.

How it works

  1. 1Open Hollow STL for Resin Printing and choose your file or enter the required input.
  2. 2Check the settings and start the process.
  3. 3The tool creates the result with temporary server-side processing.
  4. 4Download the output or copy the result when it is ready.

FAQ

›What wall thickness should I use?
2 mm suits most small and medium figures and 2.5 to 3 mm large or heavy prints; Lychee's default is 2.5 mm. Thinner walls save more resin but crack more easily during washing and curing. The report shows the thinnest wall actually left, which is never below what you set.
›Where are the drain holes placed?
Each cavity gets holes at its lowest points towards the side you mark as the base (the bottom, −Z, by default), drilled perpendicular to the wall. The second hole sits away from the first so air can enter while resin drains, which also stops the print acting as a suction cup. You can move or add holes by clicking on the model in the preview.
›How big should the holes be?
3 to 4 mm drains most models and is easy to plug; use 5 to 8 mm on large prints or with thick resin so it empties in reasonable time. Formlabs' design guide for the Form 4 gives 0.75 mm as the smallest hole that still lets resin out, which is a floor, not a target.
›What are the plugs for?
One plug per hole comes in the ZIP, 0.15 mm smaller all round so it slides in. Print them with the model, and after washing and curing glue them into the holes with a drop of resin and a second cure, so the surface is closed again.
›Why did part of my model stay solid?
A part thinner than two walls has no inside left once the walls are in place: arms, swords, thin capes and fingers stay solid. That is correct, not a failure; the report gives the share of the surface that stayed solid. Very small pockets that could not drain are filled for the same reason.
›Does it work with broken or open STL files?
Yes, within reason. The mesh is repaired first (holes closed, flipped faces fixed, overlapping parts merged). If it cannot be made into a closed solid, you get a message and no charge; run it through STL Repair and try again.
›Can I hollow OBJ or 3MF files?
Not yet: the tool takes STL. Convert OBJ, 3MF or PLY to STL first with the 3D Model Converter.
›Is my file kept?
No. It is processed on our server and deleted with the result after your download, at most two hours later if you never download. Nothing is shared or used for anything else.