diff --git a/Assets/Cryville.EEW.Unity/Map/LineRenderer.cs b/Assets/Cryville.EEW.Unity/Map/LineRenderer.cs
index 1fa398e..6191f57 100644
--- a/Assets/Cryville.EEW.Unity/Map/LineRenderer.cs
+++ b/Assets/Cryville.EEW.Unity/Map/LineRenderer.cs
@@ -13,11 +13,16 @@ namespace Cryville.EEW.Unity.Map {
 	[RequireComponent(typeof(MeshFilter))]
 	[RequireComponent(typeof(MeshRenderer))]
 	class LineRenderer : MonoBehaviour {
+		Material _sharedMaterial;
 		public Material Material {
-			get => _meshRenderer.material;
+			get => _meshRenderer.sharedMaterial;
 			set {
-				_meshRenderer.material = value;
-				_meshRenderer.material.color = m_color;
+				if (value == _sharedMaterial) return;
+				if (_sharedMaterial != null) Destroy(_meshRenderer.sharedMaterial);
+				_sharedMaterial = value;
+				if (_sharedMaterial == null) return;
+				_meshRenderer.sharedMaterial = Instantiate(_sharedMaterial);
+				_meshRenderer.sharedMaterial.color = m_color;
 			}
 		}
 
@@ -28,7 +33,7 @@ namespace Cryville.EEW.Unity.Map {
 			set {
 				if (m_color == value) return;
 				m_color = value;
-				_meshRenderer.material.color = value;
+				_meshRenderer.sharedMaterial.color = value;
 			}
 		}
 
@@ -126,12 +131,17 @@ namespace Cryville.EEW.Unity.Map {
 				_meshFilter.mesh = new();
 			}
 			_mesh = _meshFilter.mesh;
-			_meshRenderer.material.color = m_color;
+			if (_sharedMaterial == null && _meshRenderer.sharedMaterial != null) {
+				_sharedMaterial = _meshRenderer.sharedMaterial;
+				_meshRenderer.sharedMaterial = Instantiate(_sharedMaterial);
+				_meshRenderer.sharedMaterial.color = m_color;
+			}
 		}
 		void OnDestroy() {
 			if (_positions is not null)
 				ArrayPool<Vector2>.Shared.Return(_positions);
 			Destroy(_mesh);
+			Destroy(Material);
 		}
 		void LateUpdate() {
 			if (_valid) return;
diff --git a/Assets/Cryville.EEW.Unity/Map/PolygonRenderer.cs b/Assets/Cryville.EEW.Unity/Map/PolygonRenderer.cs
index 43a17ff..049ba29 100644
--- a/Assets/Cryville.EEW.Unity/Map/PolygonRenderer.cs
+++ b/Assets/Cryville.EEW.Unity/Map/PolygonRenderer.cs
@@ -11,11 +11,16 @@ namespace Cryville.EEW.Unity.Map {
 	[RequireComponent(typeof(MeshFilter))]
 	[RequireComponent(typeof(MeshRenderer))]
 	class PolygonRenderer : MonoBehaviour {
+		Material _sharedMaterial;
 		public Material Material {
-			get => _meshRenderer.material;
+			get => _meshRenderer.sharedMaterial;
 			set {
-				_meshRenderer.material = value;
-				_meshRenderer.material.color = m_color;
+				if (value == _sharedMaterial) return;
+				if (_sharedMaterial != null) Destroy(_meshRenderer.sharedMaterial);
+				_sharedMaterial = value;
+				if (_sharedMaterial == null) return;
+				_meshRenderer.sharedMaterial = Instantiate(_sharedMaterial);
+				_meshRenderer.sharedMaterial.color = m_color;
 			}
 		}
 
@@ -40,10 +45,15 @@ namespace Cryville.EEW.Unity.Map {
 				_meshFilter.mesh = new();
 			}
 			_mesh = _meshFilter.mesh;
-			_meshRenderer.material.color = m_color;
+			if (_sharedMaterial == null && _meshRenderer.sharedMaterial != null) {
+				_sharedMaterial = _meshRenderer.sharedMaterial;
+				_meshRenderer.sharedMaterial = Instantiate(_sharedMaterial);
+				_meshRenderer.sharedMaterial.color = m_color;
+			}
 		}
 		void OnDestroy() {
 			Destroy(_mesh);
+			Destroy(Material);
 		}
 		public void SetPolygon(IEnumerable<IEnumerable<PointF>> polygon) {
 			_mesh.Clear();