diff --git a/test/unit/assets/missing_texture.mtl b/test/unit/assets/missing_texture.mtl
new file mode 100644
index 0000000000..d0a94874de
--- /dev/null
+++ b/test/unit/assets/missing_texture.mtl
@@ -0,0 +1,6 @@
+newmtl m0
+Kd 1 0 0
+map_Kd does_not_exist.png
+
+newmtl m1
+Kd 0 0 1
diff --git a/test/unit/assets/missing_texture.obj b/test/unit/assets/missing_texture.obj
new file mode 100644
index 0000000000..6e70707c38
--- /dev/null
+++ b/test/unit/assets/missing_texture.obj
@@ -0,0 +1,13 @@
+mtllib missing_texture.mtl
+v 0 0 0
+v 1 0 0
+v 0 1 0
+v 1 1 0
+vt 0 0
+vt 1 0
+vt 0 1
+vt 1 1
+usemtl m0
+f 1/1 2/2 3/3
+usemtl m1
+f 2/2 4/4 3/3
diff --git a/test/unit/assets/multi_material_12.mtl b/test/unit/assets/multi_material_12.mtl
new file mode 100644
index 0000000000..eb05a5f7ab
--- /dev/null
+++ b/test/unit/assets/multi_material_12.mtl
@@ -0,0 +1,36 @@
+newmtl m00
+Kd 0.000 0.876 0.844
+
+newmtl m01
+Kd 0.500 0.518 0.999
+
+newmtl m02
+Kd 0.866 0.021 0.886
+
+newmtl m03
+Kd 1.000 0.482 0.536
+
+newmtl m04
+Kd 0.866 0.855 0.042
+
+newmtl m05
+Kd 0.500 1.000 0.463
+
+newmtl m06
+Kd 0.000 0.876 0.844
+
+newmtl m07
+Kd 0.500 0.518 0.999
+
+newmtl m08
+Kd 0.866 0.021 0.886
+
+newmtl m09
+Kd 1.000 0.482 0.536
+
+newmtl m10
+Kd 0.866 0.855 0.042
+
+newmtl m11
+Kd 0.500 1.000 0.463
+
diff --git a/test/unit/assets/multi_material_12.obj b/test/unit/assets/multi_material_12.obj
new file mode 100644
index 0000000000..3fa749b5ab
--- /dev/null
+++ b/test/unit/assets/multi_material_12.obj
@@ -0,0 +1,61 @@
+mtllib multi_material_12.mtl
+v -1.5 -1 0
+v -0.7 -1 0
+v -1.5 -0.19999999999999996 0
+v -0.5 -1 0
+v 0.30000000000000004 -1 0
+v -0.5 -0.19999999999999996 0
+v 0.5 -1 0
+v 1.3 -1 0
+v 0.5 -0.19999999999999996 0
+v 1.5 -1 0
+v 2.3 -1 0
+v 1.5 -0.19999999999999996 0
+v -1.5 0 0
+v -0.7 0 0
+v -1.5 0.8 0
+v -0.5 0 0
+v 0.30000000000000004 0 0
+v -0.5 0.8 0
+v 0.5 0 0
+v 1.3 0 0
+v 0.5 0.8 0
+v 1.5 0 0
+v 2.3 0 0
+v 1.5 0.8 0
+v -1.5 1 0
+v -0.7 1 0
+v -1.5 1.8 0
+v -0.5 1 0
+v 0.30000000000000004 1 0
+v -0.5 1.8 0
+v 0.5 1 0
+v 1.3 1 0
+v 0.5 1.8 0
+v 1.5 1 0
+v 2.3 1 0
+v 1.5 1.8 0
+usemtl m00
+f 1 2 3
+usemtl m01
+f 4 5 6
+usemtl m02
+f 7 8 9
+usemtl m03
+f 10 11 12
+usemtl m04
+f 13 14 15
+usemtl m05
+f 16 17 18
+usemtl m06
+f 19 20 21
+usemtl m07
+f 22 23 24
+usemtl m08
+f 25 26 27
+usemtl m09
+f 28 29 30
+usemtl m10
+f 31 32 33
+usemtl m11
+f 34 35 36
diff --git a/test/unit/assets/single_material.mtl b/test/unit/assets/single_material.mtl
new file mode 100644
index 0000000000..74b68eb8b4
--- /dev/null
+++ b/test/unit/assets/single_material.mtl
@@ -0,0 +1,3 @@
+newmtl only
+Kd 0.2 0.7 0.9
+Ns 40
diff --git a/test/unit/assets/single_material.obj b/test/unit/assets/single_material.obj
new file mode 100644
index 0000000000..f6397bf84e
--- /dev/null
+++ b/test/unit/assets/single_material.obj
@@ -0,0 +1,22 @@
+mtllib single_material.mtl
+v -0.5 -0.5 -0.5
+v 0.5 -0.5 -0.5
+v 0.5 0.5 -0.5
+v -0.5 0.5 -0.5
+v -0.5 -0.5 0.5
+v 0.5 -0.5 0.5
+v 0.5 0.5 0.5
+v -0.5 0.5 0.5
+usemtl only
+f 1 2 3
+f 1 3 4
+f 5 6 7
+f 5 7 8
+f 1 5 8
+f 1 8 4
+f 2 6 7
+f 2 7 3
+f 4 8 7
+f 4 7 3
+f 1 5 6
+f 1 6 2
diff --git a/test/unit/io/loadModel.js b/test/unit/io/loadModel.js
index 0c2efa9cf7..87b40d9aab 100644
--- a/test/unit/io/loadModel.js
+++ b/test/unit/io/loadModel.js
@@ -1,6 +1,7 @@
 import { mockP5, mockP5Prototype, httpMock } from '../../js/mocks';
 import loading from '../../../src/webgl/loading';
 import { Geometry } from '../../../src/webgl/p5.Geometry';
+import { vi } from 'vitest';
 
 suite('loadModel', function () {
   const invalidFile = '404file';
@@ -131,6 +132,73 @@ suite('loadModel', function () {
     }
   });
 
+  test('a single-material OBJ stays one part', async function () {
+    // eg1.obj has one real material, so it is not split
+    const model = await mockP5Prototype.loadModel(inconsistentColorObjFile);
+    assert.equal(model.parts.length, 1);
+    assert.equal(model.parts[0], model, 'the geometry is its own single part');
+  });
+
+  test('a 12-material OBJ splits into 12 parts', async function () {
+    const model = await mockP5Prototype.loadModel(
+      '/test/unit/assets/multi_material_12.obj'
+    );
+    assert.equal(model.parts.length, 12);
+    // every face still lands in exactly one part
+    const totalFaces = model.parts.reduce((s, p) => s + p.faces.length, 0);
+    assert.equal(totalFaces, model.faces.length);
+  });
+
+  test('parts get computed normals when the OBJ has none', async function () {
+    // textured.obj has no vn lines, so normals are computed before the split
+    const model = await mockP5Prototype.loadModel(
+      '/test/unit/assets/textured.obj'
+    );
+    assert.equal(model.parts.length, 2);
+    for (const part of model.parts) {
+      assert.equal(
+        part.vertexNormals.length,
+        part.vertices.length,
+        'each part has one computed normal per vertex'
+      );
+    }
+  });
+
+  test('each part carries its own localised uvs', async function () {
+    const model = await mockP5Prototype.loadModel(
+      '/test/unit/assets/textured.obj'
+    );
+    assert.equal(model.parts.length, 2);
+    for (const part of model.parts) {
+      assert.equal(
+        part.uvs.length,
+        part.vertices.length,
+        'each part has one uv per localised vertex'
+      );
+    }
+  });
+
+  test('a failed texture load warns instead of failing silently', async function () {
+    const warnSpy = vi.spyOn(console, 'warn').mockImplementation(() => {});
+    mockP5Prototype.loadImage = async () => {
+      throw new Error('Not Found');
+    };
+    try {
+      const model = await mockP5Prototype.loadModel(
+        '/test/unit/assets/textured.obj'
+      );
+      // the model still loads with both material parts
+      assert.equal(model.parts.length, 2);
+      // the failed texture is skipped, so no part carries it
+      assert.ok(model.parts.every(p => p.partState.texture == null));
+      // and the failure is surfaced, not silent
+      assert.ok(warnSpy.mock.calls.length > 0, 'a warning is emitted');
+    } finally {
+      delete mockP5Prototype.loadImage;
+      warnSpy.mockRestore();
+    }
+  });
+
   test('mixed material coloring loads model with sentinel colors for uncolored vertices', async function () {
     const model = await mockP5Prototype.loadModel(inconsistentColorObjFile);
     assert.instanceOf(model, Geometry);
diff --git a/test/unit/io/parseMtl.js b/test/unit/io/parseMtl.js
index c01ef7947a..7e094e764b 100644
--- a/test/unit/io/parseMtl.js
+++ b/test/unit/io/parseMtl.js
@@ -48,6 +48,21 @@ suite('parseMtlData', function () {
     expect(materials.a.diffuseColor).toEqual([0, 0, 0]);
     expect(Object.keys(materials)).toEqual(['a']);
   });
+
+  test('a Kd-only material parses without error', function () {
+    // the common case: a material that only sets a diffuse colour
+    const materials = parseMtlData('newmtl plain\nKd 0.2 0.4 0.6');
+    expect(materials.plain.diffuseColor).toEqual([0.2, 0.4, 0.6]);
+    expect(materials.plain.texturePath).toBeUndefined();
+  });
+
+  test('a malformed mtl does not throw', function () {
+    // an unknown token, a token missing its value, and a blank line
+    const mtl = 'newmtl weird\nKd 1 0 0\nfoo bar baz\nNs\n\nsomething_else';
+    expect(() => parseMtlData(mtl)).not.toThrow();
+    // the valid tokens around the junk are still read
+    expect(parseMtlData(mtl).weird.diffuseColor).toEqual([1, 0, 0]);
+  });
 });
 
 suite('mtlToPartState', function () {
diff --git a/test/unit/visual/cases/webgl.js b/test/unit/visual/cases/webgl.js
index ed2af5fdc6..798efa6e52 100644
--- a/test/unit/visual/cases/webgl.js
+++ b/test/unit/visual/cases/webgl.js
@@ -411,6 +411,70 @@ visualSuite('WebGL', function () {
         screenshot();
       }
     );
+    visualTest(
+      'multi-material OBJ renders each material part',
+      async function (p5, screenshot) {
+        p5.createCanvas(50, 50, p5.WEBGL);
+        // textured.obj has two materials: a cat texture and a plain colour
+        const model = await new Promise(resolve =>
+          p5.loadModel('test/unit/assets/textured.obj', resolve)
+        );
+        model.normalize();
+        p5.background(255);
+        p5.rotateX(0.4);
+        p5.rotateY(0.4);
+        p5.noStroke();
+        p5.model(model);
+        screenshot();
+      }
+    );
+    visualTest(
+      'a slice with a missing texture falls back to its colour',
+      async function (p5, screenshot) {
+        p5.createCanvas(50, 50, p5.WEBGL);
+        // missing_texture.obj: m0 has a 404 map_Kd (falls back to red), m1 blue
+        const model = await new Promise(resolve =>
+          p5.loadModel('test/unit/assets/missing_texture.obj', resolve)
+        );
+        model.normalize();
+        p5.background(255);
+        p5.rotateX(0.4);
+        p5.rotateY(0.4);
+        p5.noStroke();
+        p5.model(model);
+        screenshot();
+      }
+    );
+    visualTest(
+      'a 12-material OBJ renders every material',
+      async function (p5, screenshot) {
+        p5.createCanvas(50, 50, p5.WEBGL);
+        const model = await new Promise(resolve =>
+          p5.loadModel('test/unit/assets/multi_material_12.obj', resolve)
+        );
+        model.normalize();
+        p5.background(255);
+        p5.noStroke();
+        p5.model(model);
+        screenshot();
+      }
+    );
+    visualTest(
+      'a single-material OBJ renders through the part path',
+      async function (p5, screenshot) {
+        p5.createCanvas(50, 50, p5.WEBGL);
+        const model = await new Promise(resolve =>
+          p5.loadModel('test/unit/assets/single_material.obj', resolve)
+        );
+        model.normalize();
+        p5.background(255);
+        p5.rotateX(0.4);
+        p5.rotateY(0.4);
+        p5.noStroke();
+        p5.model(model);
+        screenshot();
+      }
+    );
   });
 
   visualSuite('vertexProperty', function () {
diff --git a/test/unit/visual/screenshots/WebGL/3DModel/a 12-material OBJ renders every material/000.png b/test/unit/visual/screenshots/WebGL/3DModel/a 12-material OBJ renders every material/000.png
new file mode 100644
index 0000000000..bb5fc67e44
Binary files /dev/null and b/test/unit/visual/screenshots/WebGL/3DModel/a 12-material OBJ renders every material/000.png differ
diff --git a/test/unit/visual/screenshots/WebGL/3DModel/a 12-material OBJ renders every material/metadata.json b/test/unit/visual/screenshots/WebGL/3DModel/a 12-material OBJ renders every material/metadata.json
new file mode 100644
index 0000000000..2d4bfe30da
--- /dev/null
+++ b/test/unit/visual/screenshots/WebGL/3DModel/a 12-material OBJ renders every material/metadata.json	
@@ -0,0 +1,3 @@
+{
+  "numScreenshots": 1
+}
\ No newline at end of file
diff --git a/test/unit/visual/screenshots/WebGL/3DModel/a single-material OBJ renders through the part path/000.png b/test/unit/visual/screenshots/WebGL/3DModel/a single-material OBJ renders through the part path/000.png
new file mode 100644
index 0000000000..49140f8bf9
Binary files /dev/null and b/test/unit/visual/screenshots/WebGL/3DModel/a single-material OBJ renders through the part path/000.png differ
diff --git a/test/unit/visual/screenshots/WebGL/3DModel/a single-material OBJ renders through the part path/metadata.json b/test/unit/visual/screenshots/WebGL/3DModel/a single-material OBJ renders through the part path/metadata.json
new file mode 100644
index 0000000000..2d4bfe30da
--- /dev/null
+++ b/test/unit/visual/screenshots/WebGL/3DModel/a single-material OBJ renders through the part path/metadata.json	
@@ -0,0 +1,3 @@
+{
+  "numScreenshots": 1
+}
\ No newline at end of file
diff --git a/test/unit/visual/screenshots/WebGL/3DModel/a slice with a missing texture falls back to its colour/000.png b/test/unit/visual/screenshots/WebGL/3DModel/a slice with a missing texture falls back to its colour/000.png
new file mode 100644
index 0000000000..211724fc49
Binary files /dev/null and b/test/unit/visual/screenshots/WebGL/3DModel/a slice with a missing texture falls back to its colour/000.png differ
diff --git a/test/unit/visual/screenshots/WebGL/3DModel/a slice with a missing texture falls back to its colour/metadata.json b/test/unit/visual/screenshots/WebGL/3DModel/a slice with a missing texture falls back to its colour/metadata.json
new file mode 100644
index 0000000000..2d4bfe30da
--- /dev/null
+++ b/test/unit/visual/screenshots/WebGL/3DModel/a slice with a missing texture falls back to its colour/metadata.json	
@@ -0,0 +1,3 @@
+{
+  "numScreenshots": 1
+}
\ No newline at end of file
diff --git a/test/unit/visual/screenshots/WebGL/3DModel/multi-material OBJ renders each material part/000.png b/test/unit/visual/screenshots/WebGL/3DModel/multi-material OBJ renders each material part/000.png
new file mode 100644
index 0000000000..f6bbe85a95
Binary files /dev/null and b/test/unit/visual/screenshots/WebGL/3DModel/multi-material OBJ renders each material part/000.png differ
diff --git a/test/unit/visual/screenshots/WebGL/3DModel/multi-material OBJ renders each material part/metadata.json b/test/unit/visual/screenshots/WebGL/3DModel/multi-material OBJ renders each material part/metadata.json
new file mode 100644
index 0000000000..2d4bfe30da
--- /dev/null
+++ b/test/unit/visual/screenshots/WebGL/3DModel/multi-material OBJ renders each material part/metadata.json	
@@ -0,0 +1,3 @@
+{
+  "numScreenshots": 1
+}
\ No newline at end of file