diff --git a/src/io/export_3mf.ts b/src/io/export_3mf.ts
new file mode 100644
index 0000000..2c5806f
--- /dev/null
+++ b/src/io/export_3mf.ts
@@ -0,0 +1,86 @@
+import UZIP from "uzip";
+import { IndexedPolyhedron } from "./common";
+import { v4 as uuidv4 } from "uuid";
+import chroma from "chroma-js";
+
+function getColorMapping(colors: chroma.Color[], projectedColors: chroma.Color[]): number[] {
+    const projectedLabs = projectedColors.map(c => c.lab());
+
+    return colors.map((targetColor, i) => {
+        const targetLab = targetColor.lab();
+
+        let closestIndex = 0;
+        let minDelta = Infinity;
+        projectedLabs.forEach((projectedLab, index) => {
+            const deltaL = targetLab[0] - projectedLab[0];
+            const deltaA = targetLab[1] - projectedLab[1];
+            const deltaB = targetLab[2] - projectedLab[2];
+            const d = Math.sqrt(deltaL * deltaL + deltaA * deltaA + deltaB * deltaB);
+            if (d < minDelta) {
+                minDelta = d;
+                closestIndex = index;
+            }
+        });
+        return closestIndex;
+    });
+}
+
+// Reverse-engineered from PrusaSlicer / BambuStudio's output.
+const PAINT_COLOR_MAP = ['', '8', '0C', '1C', '2C', '3C', '4C', '5C', '6C', '7C', '8C', '9C', 'AC', 'BC', 'CC', 'DC'];
+
+export function exportOffTo3MF(data: IndexedPolyhedron, extruderColors?: chroma.Color[]): Blob {
+    const objectUuid = uuidv4();
+    const buildUuid = uuidv4();
+    const paintColorByColorIndex = extruderColors &&
+        getColorMapping(data.colors.map(c => chroma.rgb(...c)), extruderColors).map(i => PAINT_COLOR_MAP[i]);
+    
+    const archive = {
+        // _rels/.rels
+        '[Content Types].xml': new TextEncoder().encode([
+            '<?xml version="1.0" encoding="utf-8"?>',
+            '<Types xmlns="http://schemas.openxmlformats.org/package/2006/content-types">',
+                '<Default Extension="model" ContentType="application/vnd.ms-package.3dmanufacturing-3dmodel+xml"/>',
+            '</Types>',
+        ].join('\n')),
+        '3D/3dmodel.model': new TextEncoder().encode([
+            '<?xml version="1.0" encoding="utf-8"?>',
+            '<model unit="millimeter" xml:lang="en-US" xmlns="http://schemas.microsoft.com/3dmanufacturing/core/2015/02" xmlns:p="http://schemas.microsoft.com/3dmanufacturing/production/2015/06">',
+                '<meta name="BambuStudio:3mfVersion" value="1"/>',
+                '<meta name="slic3rpe:Version3mf" value="1"/>',
+                '<meta name="slic3rpe:MmPaintingVersion" value="1"/>',
+                '<resources>',
+                    '<basematerials id="2">',
+                    ...data.colors.map((color, i) => `<base name="color_${i}" displaycolor="#${chroma.rgb(...color).hex()}"/>`),
+                    '</basematerials>',
+                    `<object id="1" name="OpenSCAD Model" type="model" p:UUID="${objectUuid}" pid="2" pindex="0">`,
+                        '<mesh>',
+                            '<vertices>',
+                                ...data.vertices.map((vertex, i) => `<vertex x="${vertex.x}" y="${vertex.y}" z="${vertex.z}" />`),
+                            '</vertices>',
+                            '<triangles>',
+                                ...data.faces.map((face, i) => {
+                                    const { vertices, colorIndex } = face;
+                                    if (vertices.length != 3) throw new Error('Face must have 3 vertices');
+                                    const attrs = vertices.map((v, i) => `v${i + 1}="${v}"`);
+                                    if (colorIndex > 0) {
+                                        attrs.push(`pid="2" p1="${colorIndex}"`);
+                                    }
+                                    const paintColor = paintColorByColorIndex && paintColorByColorIndex[colorIndex];
+                                    if (paintColor) {
+                                        attrs.push(`paint_color="${paintColor}"`);
+                                    }
+                                    return `<triangle ${attrs.join(' ')} />`;
+                                }),
+                            '</triangles>',
+                        '</mesh>',
+                    '</object>',
+                '</resources>',
+                `<build p:UUID="${buildUuid}}">`,
+                    `<item objectid="1" p:UUID="${objectUuid}"/>`,
+                '</build>',
+            '</model>',
+        ].join('\n')),
+    };
+    return new Blob([UZIP.encode(archive)], {type: 'model/3mf'});
+}
+