Blender and Unity handoff

Kiln exports GLB files. The established exporter is still the default. Use the normal CLI/MCP workflow first; choosing Blender or Unity does not require an exporter switch. The experimental Three.js exporter is included in builds containing this integration, but older installed releases do not gain it by setting an environment variable.

For delivery files, see editable and runtime export profiles. Converter selection applies when generating a GLB; the delivery profile applies to an already-saved revision. Keep an editable ZIP for authoring and compare runtime delivery when duplicate review data makes an animated GLB larger. Either converter works with either delivery profile; neither choice automatically enables compression.

Choose the import route#

For Unity, follow the installed importer’s setup instructions rather than assuming that copying a GLB into Assets is sufficient. Our tested combination is Unity 6000.2.3f1, Built-in RP and glTFast 6.20.0. Blender checks used 5.2.0 LTS. These are measured profiles, not requirements to downgrade another working project or claims about every pipeline.

glTFast supports more than base colour, including double-sided surfaces, but individual material extensions have pipeline-specific limits. Preserve glTF-compatible materials when importing; replacing them with a different shader can change the result. See the glTFast feature matrix.

When to try the experimental exporter#

Try a comparison if the default export reports a feature it cannot preserve, or the task requires candidate capabilities such as vertex colours, extra UV sets, skin/morph data or additional physical-material extensions. It can also help isolate an exporter defect from an importer problem. It is not an automatic fix for all Blender/Unity issues.

Keep the source and baseline GLB. Write the candidate to a different filename, import both with the same consumer settings, and report what actually changed. Agents should identify the candidate as experimental when using it. Do not silently switch a shared host or claim an untested importer works. If the default already meets the task, there is no need to switch.

CLI: compare without changing the machine configuration#

In an asset workspace, use its existing kiln.mjs launcher. These PowerShell commands scope the selection to the current process and restore its previous value even if export fails:

$previousExporter = $env:KILN_GLTF_EXPORTER
try {
    $env:KILN_GLTF_EXPORTER = 'legacy'
    node kiln.mjs render asset.kiln.js --out asset-baseline.glb --views asset-baseline.png --render gpu
    if ($LASTEXITCODE -ne 0) { throw 'Baseline export failed' }

    $env:KILN_GLTF_EXPORTER = 'three'
    node kiln.mjs render asset.kiln.js --out asset-experimental.glb --views asset-experimental.png --render gpu
    if ($LASTEXITCODE -ne 0) { throw 'Experimental export failed' }
} finally {
    if ($null -eq $previousExporter) { Remove-Item Env:KILN_GLTF_EXPORTER -ErrorAction SilentlyContinue }
    else { $env:KILN_GLTF_EXPORTER = $previousExporter }
}

--render gpu requires a working GPU renderer and fails if unavailable; it does not accept a CPU fallback as material evidence. See Kiln’s GPU setup. In a repository clone, use node dist/cli.mjs instead of node kiln.mjs, after bun install --frozen-lockfile and bun run build:runtime. For an installed distribution, use the CLI launcher you already use, from a distribution containing this feature.

In a POSIX shell, selection can be scoped to each invocation:

KILN_GLTF_EXPORTER=legacy node kiln.mjs render asset.kiln.js --out asset-baseline.glb --views asset-baseline.png --render gpu
KILN_GLTF_EXPORTER=three node kiln.mjs render asset.kiln.js --out asset-experimental.glb --views asset-experimental.png --render gpu

MCP: select at host startup#

The exporter is not a kiln_render tool argument. Set KILN_GLTF_EXPORTER=three in the environment of the existing Kiln MCP server entry, preserving its command, arguments and other settings. For hosts using an env object, add this field to that object:

{ "KILN_GLTF_EXPORTER": "three" }

Restart/reconnect that server so it captures the new setting. Continue using the same tools and saved programRef values; build caches distinguish backends. To restore the established exporter, remove that field or set it to legacy, then restart/reconnect again. If an agent cannot configure the host, it must not claim to have switched it; a separate CLI comparison is available when the agent has terminal access.

New workspaces receive this guide through the authoring/QA skills. Existing workspace skills are local copies; updating the engine or running workspace repair does not automatically replace edited skills. Consult the updated runtime documentation when working in an older workspace.

Geometry, materials and moving parts#

• Backfaces: a single-sided sheet disappearing from behind is expected culling. Use a double-sided material for an intentionally thin surface when the importer supports it. Author actual thickness when the object needs thickness, collision or different surfaces; do not automatically extrude every quad to hide an import problem.
• Pivots: give moving groups stable, descriptive names such as Joint_VaneSwivel, with visible geometry beneath them, for example Mesh_Pennant. This is an authoring convention, not a required engine prefix. Preserve names across revisions and report the actual part paths.
• Unity root names: glTFast can replace a static single-root name with the asset filename. Check its Scene Object Creation setting; test Always if an authored root under a wrapper is needed. Resolve parts relative to the imported root instead of assuming one universal path.
• Animation: play the imported clip and inspect intermediate poses. A clip existing in the file is not proof that its target moves. Check skin/morph deformation where applicable.
• FBX: in Blender’s FBX export, leave the experimental Apply Transform option (bake_space_transform) disabled for the tested nested-part route. This is separate from Bake Animation. Reimport the FBX and check offsets; materials and sidedness can still change. See Blender’s option documentation.

Measured LOD import behavior#

On 2026-09-30, headless structural checks imported 13 static vegetation and freight GLBs from a prior 0.9 candidate. Both tested destinations exposed the expected LOD0 triangle counts in their active scenes. The results apply to those files and installed importer versions, not every feature in the current development tree.

That first check established structural import, not automatic LOD switching, material appearance or player traversal. Its fixtures had no source animations, textures, skins or morph targets. For runtime LOD switching, arrange the tiers through the destination’s supported import or runtime workflow and verify the transitions there; the presence of MSFT_lod alone does not establish that the consumer switches levels.

Kiln’s viewer has a global Level selector and per-part overrides for independent LOD chains. The global selector applies one index to every chain, clamping to each chain’s available levels. Per-part controls let you inspect combinations such as a tractor’s LOD1 body with LOD0 wheels; the global selector then reads Mixed. Live Review’s current and pinned assets have independent controls. A body’s LOD1 and a wheel’s LOD1 can represent different switching thresholds, so these controls are manual inspection aids and do not simulate a shared distance. Verify the combinations needed by the destination, including geometry outside the selected body subtree.

Animated assets and visibility: tested destination limits#

A later 2026-09-30 check used the revised campus plants, 24 Foundry assets with declared LOD chains, and an animation/visibility fixture from each Kiln exporter: 39 files in total. Blender imported all 39. The tested Unity/glTFast profile imported 38 canonical files; the AMR’s animation channel targeting its detached lower-tier deck caused an importer assertion. Preserve the canonical file. For a destination that needs only LOD0, a separate derivative can retain the default scene and filter animation channels whose targets are outside it. That explicit AMR derivative imported with both detailed-level clips working. Do not remove the coarse animation from the editable master merely to accommodate this importer. Lower-tier runtime animation needs a destination workflow that imports those nodes.

Both tested importers ignored KHR_node_visibility. A fixture containing 46 intended visible triangles and a hidden 12-triangle cube drew all 58. The Foundry container’s hidden wafer payload also became active. Apply the authored visibility in the destination, or prepare an explicit delivery derivative that omits hidden subtrees and their unreachable animation targets. Keep the source and canonical GLB. Selecting the other Kiln exporter did not change this result.

Intermediate animation samples matter too. Blender reproduced the tested eased translation. In glTFast 6.20.0, the same standard cubic curve differed between endpoints: at 25% of a one-second movement from Y=0.5 to Y=1.5, the intended value was 0.65625, but the imported clip sampled 0.605893. Both Kiln exporters produced this result. A separate Unity clip copy with the cubic keys’ weightedMode set to WeightedMode.None matched all five tested times while retaining the imported tangents. Apply this only to curves known to originate as glTF cubic Hermite curves; it is not a general instruction to alter authored Unity curves.

For Blender animation inspection, choose each imported action separately and use its actual frame range. Its NLA strips can start at frame 1. Enable the glTF add-on’s Animation UI before importing to retain the glTF rest pose. Muting an action alone can leave animated-property defaults rather than that rest pose. Check the rest pose as well as intermediate clip positions before judging hierarchy or fit.

These results qualify the named importer profiles and fixtures. They do not establish texture, skin, morph, other render-pipeline or arbitrary cubic-curve compatibility.

A Windows standalone player built with the same Unity profile rendered all 39 test cases on Direct3D 11 with an RTX 3070, with supported shaders and no missing-material pink. It exercised 49 clips and verified movement of their authored targets. This player used the explicit LOD0 AMR derivative and the two visibility-fixture derivatives; the canonical Foundry container still exposed the visibility limitation described above. A separate all-tier conifer derivative wired into a Unity LODGroup rendered 1,376, 184 and 48 triangles when each level was forced. This demonstrates an explicit destination setup, not automatic importer-created LODs or qualified distance thresholds. Material appearance and silhouette remain part of owner review.

Known experimental limits#

• Rotated nonuniform Three.js UV scaling and manually sheared/perspective UV matrices are rejected when they cannot be represented losslessly in glTF texture TRS. Do not remove the transform or silently change the asset just to make export succeed.
• Textured headless candidate exports need the optional native canvas dependency. If it is unavailable, fix the installation or report the limitation; textures are not silently dropped.
• Lines/points are outside the candidate’s qualified triangle/sprite pipeline.
• Preserved emissive/unlit properties may look different from older exports that dropped them.
• Emissive exports as colour times intensity. Within 0..1 that is emissiveFactor; brighter emission adds KHR_materials_emissive_strength, which an importer without that extension shows at the normalised colour.
• Declared LOD sets export as MSFT_lod chains: LOD0 stays in the scene carrying extensions.MSFT_lod.ids and extras.MSFT_screencoverage, and the lower levels are off-scene nodes whose transforms are relative to LOD0’s parent. An importer without the extension shows LOD0 only, as three.js GLTFLoader 0.186 does. The measured Blender and glTFast behavior is recorded above; automatic threshold switching still needs destination qualification. An imported GLB’s chains survive save, optimisation and export too. GPU instancing skips a file with chains, and full optimisation falls back to palette.
• More extensions in a valid GLB do not guarantee support in every importer or shader. GPU appearance, runtime-loaded shader inclusion, compression codecs and other render pipelines need their own checks. This option does not change KTX2 defaults or fix unsupported Node versions.

Delivery checklist for users and agents#

Record the source revision, chosen exporter, delivered GLB, consumer/importer versions and render pipeline. Check scale and orientation alongside a known object; hierarchy and pivots; front/back visibility; materials/textures; and animation/deformation. For Unity delivery, exercise a player build as well as the editor. Say which checks were not run. Keep the baseline and source so a consumer-specific problem can be reproduced without regenerating the asset.