diff --git a/web-ifc-three/src/IFC/components/subsets/SubsetCreator.ts b/web-ifc-three/src/IFC/components/subsets/SubsetCreator.ts
index 1d5a915..b7a0b70 100644
--- a/web-ifc-three/src/IFC/components/subsets/SubsetCreator.ts
+++ b/web-ifc-three/src/IFC/components/subsets/SubsetCreator.ts
@@ -73,17 +73,15 @@ export class SubsetCreator {
     private constructSubsetByMaterial(config: SubsetConfig, subsetID: string) {
         const model = this.state.models[config.modelID].mesh;
         const newIndices = { count: 0 };
+        const indicesByMaterial = SubsetUtils.getAllIndicesByMaterial(config.ids, this.items.map[config.modelID]);
         for (let i = 0; i < model.geometry.groups.length; i++) {
-            this.insertNewIndices(config, subsetID, i, newIndices);
+            this.insertNewIndices(config, subsetID, i, newIndices, indicesByMaterial[i] || []);
         }
     }
 
     // If this subset has original materials, insert indices in correct position and update groups
     // Otherwise, just insert indices at any position
-    private insertNewIndices(config: SubsetConfig, subsetID: string, materialIndex: number, newIndices: any) {
-        const items = this.items.map[config.modelID];
-        const indicesOfOneMaterial = SubsetUtils.getAllIndicesOfGroup(config.modelID, config.ids, materialIndex, items) as number[];
-
+    private insertNewIndices(config: SubsetConfig, subsetID: string, materialIndex: number, newIndices: any, indicesOfOneMaterial: number[]) {
         if (!config.material) {
             this.insertIndicesAtGroup(subsetID, indicesOfOneMaterial, materialIndex, newIndices);
         } else {
@@ -116,4 +114,4 @@ export class SubsetCreator {
             group.count = 0;
         });
     }
-}
\ No newline at end of file
+}
diff --git a/web-ifc-three/src/IFC/components/subsets/SubsetUtils.ts b/web-ifc-three/src/IFC/components/subsets/SubsetUtils.ts
index cedd1e3..0e3fd7b 100644
--- a/web-ifc-three/src/IFC/components/subsets/SubsetUtils.ts
+++ b/web-ifc-three/src/IFC/components/subsets/SubsetUtils.ts
@@ -1,5 +1,21 @@
 export class SubsetUtils {
 
+    static getAllIndicesByMaterial(ids: number[], items: any) {
+        const indicesByMaterial: number[][] = [];
+        for (const expressID of ids) {
+            const entry = items.map.get(expressID);
+            if (!entry) continue;
+            for (const materialID of Object.keys(entry)) {
+                const materialIndex = Number(materialID);
+                const value = entry[materialIndex];
+                if (!value) continue;
+                if (!indicesByMaterial[materialIndex]) indicesByMaterial[materialIndex] = [];
+                SubsetUtils.getIndexChunk(value, indicesByMaterial[materialIndex], materialIndex, items, true);
+            }
+        }
+        return indicesByMaterial;
+    }
+
     // If flatten, all indices are in the same array; otherwise, indices are split in subarrays by material
     static getAllIndicesOfGroup(modelID: number, ids: number[], materialIndex: number, items: any, flatten = true) {
         const indicesByGroup: any = [];
@@ -28,4 +44,4 @@ export class SubsetUtils {
             }
         }
     }
-}
\ No newline at end of file
+}
diff --git a/web-ifc-three/test/IFC/Components/SubsetUtils.test.ts b/web-ifc-three/test/IFC/Components/SubsetUtils.test.ts
new file mode 100644
index 0000000..0540252
--- /dev/null
+++ b/web-ifc-three/test/IFC/Components/SubsetUtils.test.ts
@@ -0,0 +1,27 @@
+import {SubsetUtils} from "../../../src/IFC/components/subsets/SubsetUtils";
+
+describe("SubsetUtils", () => {
+
+    test("groups indices by material with one map lookup per express ID", () => {
+
+        const sourceMap = new Map<number, any>([
+            [7, {0: [0, 1, 4, 4], 2: [6, 7]}],
+            [8, {0: [5, 5], 1: [2, 3]}],
+        ]);
+        const items = {
+            indexCache: Uint32Array.from([10, 11, 12, 13, 14, 15, 16, 17]),
+            map: {
+                get: jest.fn((id: number) => sourceMap.get(id))
+            }
+        };
+
+        const result = SubsetUtils.getAllIndicesByMaterial([7, 8, 404], items);
+
+        expect(items.map.get).toHaveBeenCalledTimes(3);
+        expect(result[0]).toEqual([10, 11, 14, 15]);
+        expect(result[1]).toEqual([12, 13]);
+        expect(result[2]).toEqual([16, 17]);
+        expect(result[3]).toBeUndefined();
+        expect(result[0]).toEqual(SubsetUtils.getAllIndicesOfGroup(0, [7, 8, 404], 0, items));
+    });
+});