What's the minimum wall thickness for hollow miniatures?

2mm for small-to-medium models, 3mm for large monsters and terrain. Below 2mm the wall flexes during cure and warps; thin-walled hollow prints also fail more often during printing due to the suction force during peel cycles.

Do I need to hollow infantry-scale models?

No. The resin savings on 28-32mm infantry are minimal -- maybe a few cents per model -- and you lose structural rigidity that matters for handling and play. Hollowing is for models over 50mm tall, terrain, monsters, vehicles, and busts.

How many drain holes do I need?

Two minimum per hollow cavity. One hole alone creates a vacuum that prevents resin from flowing out -- you need a second hole to break the seal. Three holes on tall, narrow models (one near the top for air relief) drain faster and more cleanly.

Will hollow miniatures still hold up to tabletop use?

At 2-3mm wall thickness, yes. Hollow resin prints with proper walls and infill (or no infill on smaller models) are tabletop-durable. The failure mode for hollow prints is usually trapped uncured resin leaking later, not structural failure during play.

Can I hollow models in Chitubox Free?

Yes. Chitubox Free includes basic hollowing with manual drain hole placement. Chitubox Pro adds automatic drain hole detection and cleaner offset hollowing. Lychee Pro has the cleanest hollow tool of the three but requires a subscription. Free is enough for occasional hollowing.

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How to Hollow Resin Miniatures in Lychee and Chitubox (With Drain Holes)

Walk through hollowing resin miniatures in Lychee and Chitubox. Wall thickness, drain hole placement, infill, and the trade-offs that matter for tabletop printing.

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Hollowing is the resin printer’s free resin-saving trick. Take a solid model, scoop out the inside, leave a 2-3mm shell, drop a couple of holes for drainage. A bust that used to take 80g of resin now takes 30g. Multiply that across a year of printing terrain and statues and the savings get real.

It’s also where a lot of beginners create their own failures. A model hollowed without drain holes traps liquid resin that leaks later. A model hollowed at 1mm wall thickness warps during cure. A drain hole placed on the side of a model serves no function at all because resin doesn’t flow uphill.

This guide walks through hollowing in both Lychee Slicer and Chitubox, covering wall thickness, drain hole placement, and the trade-offs that actually matter. If you’re still getting your slicer set up, start with the complete beginner’s guide to resin printing first.

When to Hollow (and When Not to)

Hollow these:

Anything over 50mm tall — large characters, statues, busts, monsters
Terrain — buildings, ruins, walls, anything with significant interior volume
Vehicles — tanks, mechs, transports
Large monsters and dragons — wherever wall-to-volume is poor

Don’t hollow these:

Infantry at 28-32mm scale — the resin you save isn’t worth the structural compromise
Thin or fragile characters — gracile mages, archers with extended limbs, anything where the wall would end up under 2mm
Models with lots of fine surface relief — hollow tools can punch through walls where geometry is thin

I run a rough mental check before opening the hollow tool: if the model is solid enough that a poorly-placed drain hole would visibly damage it, I skip hollowing. The minutes spent fixing a damaged print is more than the cost of the resin I would have saved.

Step 1 — Orient the Model First

Hollowing references your model’s current orientation when placing drain holes. If you hollow first, then rotate, your drain holes end up wherever the rotation puts them — which is rarely at a low point anymore.

Always orient the model on the build plate before hollowing. For miniatures, that usually means tilted back 30-45 degrees with the model’s center of mass moved off-axis so the print peels cleanly off the FEP layer by layer.

Once oriented, generate or skip supports later — hollowing happens before support generation in the workflow.

Step 2 — Open the Hollow Tool

In Lychee, the hollow tool is in the left toolbar under Hollow. Lychee Free has basic hollowing; Lychee Pro adds automatic drain hole placement and the offset mode that gives the cleanest interior surface.

In Chitubox, the hollow tool is in the left toolbar (icon looks like a sliced sphere). Chitubox Free has manual hollowing with manual drain hole placement; Chitubox Pro adds the cleaner offset hollowing and automatic drain hole tools.

The interfaces are similar enough that the rest of this guide applies to either slicer.

Step 3 — Set Wall Thickness

Wall thickness is the most important hollowing setting. Get this wrong and everything downstream — drain placement, print success, model durability — falls apart.

2mm wall thickness — My default for small-to-medium hollow models. Characters at 54mm scale, monsters up to fist-size, small terrain pieces. Resin savings are significant and the wall holds shape during cure.

3mm wall thickness — Large monsters, dragons, vehicles, terrain over 75mm in any dimension, busts. The extra mm adds rigidity that matters when the model is large enough to flex.

1.5mm or below — Don’t. Walls under 2mm flex during cure, warp during washing, and crack under handling. The resin you save isn’t worth the failure rate.

In both Lychee and Chitubox, wall thickness is the top setting in the hollow dialog. Type the number; don’t use the slider — sliders are sloppy.

Step 4 — Smooth vs. Accurate Hollow Mode

Most slicers offer two hollowing methods:

Smooth (offset) — The wall is offset uniformly from the outer surface. Fast to compute, smooth interior, works well for organic shapes. This is my default for characters, monsters, terrain, anything with curved surfaces.

Accurate (precise) — The wall preserves the exact geometry of the outer surface, including sharp interior corners. Slower to compute, used for hard-surface models where the interior shape matters — vehicles with internal compartments, terrain with detailed interior architecture.

For most miniatures, smooth mode is fine. Accurate mode is rarely worth the extra computation time.

Step 5 — Skip Infill Unless You Need It

Both Lychee Pro and Chitubox Pro let you add internal lattice infill — gyroid, honeycomb, or grid patterns that fill the hollow cavity with thin internal structure for rigidity.

Skip it for most miniatures.

Internal infill traps uncured resin. Even with good drain holes, lattice patterns create pockets that don’t drain or wash properly. The trapped resin slowly leaks later, ruining paint jobs and creating safety hazards.

The exceptions:

Very large models (100mm+ tall) — wall flex during cure becomes a real concern; light gyroid at 5-8% adds rigidity
Terrain that will be glued together — internal infill helps the joints hold

For everything else, leave infill off.

Step 6 — Drain Holes (The Part That Actually Matters)

Drain holes are where most hollowing mistakes happen. A model hollowed with bad drain placement is worse than a solid model — it traps resin that leaks for weeks afterward.

Minimum: two drain holes per cavity.

One hole creates a vacuum. Liquid resin doesn’t flow uphill, and the cavity stays sealed by atmospheric pressure if there’s no second opening to let air in. Two holes break the vacuum and let resin actually drain.

Hole diameter: 2.5-3.5mm.

Smaller than 2.5mm and the hole is too easy to plug with cured resin during the wash cycle. Larger than 3.5mm and you create a visible, hard-to-hide opening that’s a pain to fill before painting.

Position: at the lowest points in print orientation.

This is the rule everyone gets wrong. The lowest point in print orientation is not the bottom of the model as it stands on a base. It’s the lowest point as the model is tilted on the build plate. After you orient the model at 30-45 degrees, the “low point” is somewhere on the side that hangs lowest during printing.

Rotate the model in the slicer preview after placing drain holes and confirm each one sits at a true low point. If a drain hole is on a side wall above the lowest point, resin pools below it and never drains.

Third hole for air relief on tall, narrow models.

Tall busts, lighthouse terrain, anything with a narrow internal cavity benefits from a third hole near the top for air relief. Two holes at the bottom alone can still struggle to drain if the cavity is tall and narrow — the air relief hole lets atmospheric pressure into the top while resin flows out the bottom.

Step 7 — Slice and Inspect

After hollowing and placing drain holes, slice the model and scroll through the layer preview from bottom to top.

What to check:

Wall thickness uniform — no spots where the wall thinned below the target
Drain holes appear — visible as gaps in the wall at the expected positions
No floating geometry — if the hollow tool created any disconnected internal structures, the slicer will flag islands
Interior reasonably clean — for accurate mode, confirm the interior doesn’t have spikes or artifacts the hollow tool generated

Fix anything that looks wrong before printing. A hollow defect found in the layer preview takes 10 seconds to fix; one found in the print costs you the print and the resin in it.

Step 8 — Print, Drain, and Wash Thoroughly

After printing, the most important step is the one most beginners skip:

Drain the model over the vat before removing it from the build plate.

Use a build plate scraper to gently lift the model off the plate while keeping it tilted drain-hole-down over the vat. Hold for 30-60 seconds and let trapped uncured resin run out. You’ll see a meaningful pour for the first 15-20 seconds.

Then wash thoroughly.

Hollow models need longer wash cycles than solid models. The interior cavity traps uncured resin that the wash solution has to reach. Run an extra wash cycle (15-20 minutes total) and verify by feel that the drain holes are clear and the interior surface isn’t tacky.

If you smell resin on the model after curing, it’s still got uncured resin trapped inside. Re-wash and re-cure. This is also why proper ventilation and PPE matter — uncured resin keeps off-gassing until it’s fully removed and cured.

Common Hollowing Mistakes

In rough order of how often I’ve made them:

Hollowing infantry that didn’t need it. Negligible resin savings, lost structural rigidity, occasional fragile failures.
One drain hole instead of two. The vacuum holds resin inside. Always two.
Drain holes on side walls, not low points. Resin pools below and never drains.
Wall thickness under 2mm. Walls flex during cure, warp during washing.
Adding internal infill on a model that didn’t need it. Traps resin, leaks later.
Skipping the drain step after print. Resin trapped inside makes its way out during painting or display.
Re-orienting after hollowing. Drain holes end up in the wrong place.

Fix the first three and your hollow prints will be reliable. The rest are refinements.

When to Print Solid Instead

Hollowing isn’t always the right call. There are models where the time spent setting up a clean hollow is more than the resin cost of just printing solid:

Single 28mm character — print solid
Small terrain object under 30mm in any dimension — print solid
Anything with extremely thin features that would compromise wall integrity — print solid
Anything you’re printing once and need fast — print solid

The calculation gets clearer with practice. After a few months of resin printing, you’ll have a gut sense for when hollowing pays off and when it doesn’t. Until then: hollow large stuff, print small stuff solid, and use this guide for the in-between.

Pair hollowing with the right resin choice and the cost-per-model on big terrain drops to where you can afford to actually populate a table.