diff --git a/Assets/UniGLTF/Runtime/Extensions/IndexExtensions.cs b/Assets/UniGLTF/Runtime/Extensions/IndexExtensions.cs
index 7599e5b95..e855768a5 100644
--- a/Assets/UniGLTF/Runtime/Extensions/IndexExtensions.cs
+++ b/Assets/UniGLTF/Runtime/Extensions/IndexExtensions.cs
@@ -15,5 +15,24 @@ namespace UniGLTF
             }
             return true;
         }
+
+        public static bool HasValidIndex(this int? self, int collectionLength)
+        {
+            if (!self.HasValue)
+            {
+                return false;
+            }
+            if (self.Value < 0)
+            {
+                // 古いモデルで index の無効値に -1 を使っている場合がある
+                return false;
+            }
+            if (self.Value >= collectionLength)
+            {
+                // ついでに上限もチェック
+                return false;
+            }
+            return true;
+        }
     }
 }
diff --git a/Assets/UniGLTF/Runtime/UniGLTF/IO/ImporterContext.cs b/Assets/UniGLTF/Runtime/UniGLTF/IO/ImporterContext.cs
index fba947b0e..a2605d732 100644
--- a/Assets/UniGLTF/Runtime/UniGLTF/IO/ImporterContext.cs
+++ b/Assets/UniGLTF/Runtime/UniGLTF/IO/ImporterContext.cs
@@ -49,7 +49,8 @@ namespace UniGLTF
                 Data.MigrationFlags.IsRoughnessTextureValueSquared);
             MaterialFactory = new MaterialFactory(ExternalObjectMap
                 .Where(x => x.Value is Material)
-                .ToDictionary(x => x.Key, x => (Material)x.Value));
+                .ToDictionary(x => x.Key, x => (Material)x.Value),
+                MaterialDescriptorGenerator.GetGltfDefault());
             AnimationClipFactory = new AnimationClipFactory(ExternalObjectMap
                 .Where(x => x.Value is AnimationClip)
                 .ToDictionary(x => x.Key, x => (AnimationClip)x.Value));
@@ -285,14 +286,7 @@ namespace UniGLTF
                 throw new ArgumentNullException();
             }
 
-            if (Data.GLTF.materials == null || Data.GLTF.materials.Count == 0)
-            {
-                // no material. work around.
-                // TODO: https://www.khronos.org/registry/glTF/specs/2.0/glTF-2.0.html#default-material
-                var param = MaterialDescriptorGenerator.GetGltfDefault();
-                await MaterialFactory.LoadAsync(param, TextureFactory.GetTextureAsync, awaitCaller);
-            }
-            else
+            if (Data.GLTF.materials != null)
             {
                 for (int i = 0; i < Data.GLTF.materials.Count; ++i)
                 {
@@ -314,7 +308,17 @@ namespace UniGLTF
             using (MeasureTime("BuildMesh"))
             {
                 var meshWithMaterials = await MeshUploader.BuildMeshAndUploadAsync(awaitCaller, meshData,
-                    (int? materialIndex) => materialIndex.HasValidIndex() ? MaterialFactory.GetMaterial(materialIndex.Value) : null);
+                    (int? materialIndex) =>
+                    {
+                        if (materialIndex.HasValidIndex())
+                        {
+                            return MaterialFactory.GetMaterial(materialIndex.Value);
+                        }
+                        else
+                        {
+                            return MaterialFactory.DefaultMaterial;
+                        }
+                    });
                 var mesh = meshWithMaterials.Mesh;
 
                 // mesh name
diff --git a/Assets/VRM10/Runtime/IO/Vrm10Importer.cs b/Assets/VRM10/Runtime/IO/Vrm10Importer.cs
index e75572cb6..352e8807d 100644
--- a/Assets/VRM10/Runtime/IO/Vrm10Importer.cs
+++ b/Assets/VRM10/Runtime/IO/Vrm10Importer.cs
@@ -240,7 +240,7 @@ namespace UniVRM10
                     continue;
                 }
 
-                CreateRenderer(node, go, map, MaterialFactory.Materials);
+                CreateRenderer(node, go, map, MaterialFactory);
                 await awaitCaller.NextFrame();
             }
         }
@@ -802,8 +802,7 @@ namespace UniVRM10
         /// <summary>
         /// MeshFilter + MeshRenderer もしくは SkinnedMeshRenderer を構築する
         /// </summary>
-        public static Renderer CreateRenderer(VrmLib.Node node, GameObject go, ModelMap map,
-            IReadOnlyList<VRMShaders.MaterialFactory.MaterialLoadInfo> materialLoadInfos)
+        public static Renderer CreateRenderer(VrmLib.Node node, GameObject go, ModelMap map, MaterialFactory materialFactory)
         {
             Renderer renderer = null;
             var hasBlendShape = node.MeshGroup.Meshes[0].MorphTargets.Any();
@@ -842,11 +841,11 @@ namespace UniVRM10
                     {
                         if (x.Material.HasValidIndex())
                         {
-                            return materialLoadInfos[x.Material.Value].Asset;
+                            return materialFactory.Materials[x.Material.Value].Asset;
                         }
                         else
                         {
-                            return null;
+                            return materialFactory.DefaultMaterial;
                         }
                     }
                 ).ToArray();
@@ -858,11 +857,11 @@ namespace UniVRM10
                 {
                     if (x.Submeshes[0].Material.HasValidIndex())
                     {
-                        return materialLoadInfos[x.Submeshes[0].Material.Value].Asset;
+                        return materialFactory.Materials[x.Submeshes[0].Material.Value].Asset;
                     }
                     else
                     {
-                        return null;
+                        return materialFactory.DefaultMaterial;
                     }
                 }
                 ).ToArray();
diff --git a/Assets/VRMShaders/GLTF/IO/Runtime/Material/Importer/MaterialFactory.cs b/Assets/VRMShaders/GLTF/IO/Runtime/Material/Importer/MaterialFactory.cs
index 882818fbb..0e578c92c 100644
--- a/Assets/VRMShaders/GLTF/IO/Runtime/Material/Importer/MaterialFactory.cs
+++ b/Assets/VRMShaders/GLTF/IO/Runtime/Material/Importer/MaterialFactory.cs
@@ -1,6 +1,5 @@
 using System;
 using System.Collections.Generic;
-using System.Linq;
 using System.Threading.Tasks;
 using UnityEngine;
 
@@ -13,9 +12,33 @@ namespace VRMShaders
     {
         private readonly IReadOnlyDictionary<SubAssetKey, Material> m_externalMap;
 
-        public MaterialFactory(IReadOnlyDictionary<SubAssetKey, Material> externalMaterialMap)
+        MaterialDescriptor m_defaultMaterialParams;
+
+        /// <summary>
+        /// gltfPritmitive.material が無い場合のデフォルトマテリアル
+        /// https://www.khronos.org/registry/glTF/specs/2.0/glTF-2.0.html#default-material
+        /// </summary>
+        Material m_defaultMaterial;
+
+        public Material DefaultMaterial
+        {
+            get
+            {
+                if (m_defaultMaterial == null)
+                {
+                    // default material にバリエーションがある？
+                    var task = LoadAsync(m_defaultMaterialParams, (_x, _y) => Task.FromResult<Texture>(null), new ImmediateCaller());
+                    task.Wait();
+                    m_defaultMaterial = task.Result;
+                }
+                return m_defaultMaterial;
+            }
+        }
+
+        public MaterialFactory(IReadOnlyDictionary<SubAssetKey, Material> externalMaterialMap, MaterialDescriptor defaultMaterialParams)
         {
             m_externalMap = externalMaterialMap;
+            m_defaultMaterialParams = defaultMaterialParams;
         }
 
         public struct MaterialLoadInfo