diff --git a/js/Bounds3.ts b/js/Bounds3.ts
index 4ed2912..6fe1462 100644
--- a/js/Bounds3.ts
+++ b/js/Bounds3.ts
@@ -18,7 +18,7 @@ import IOType from '../../tandem/js/types/IOType.js';
 import NumberIO from '../../tandem/js/types/NumberIO.js';
 import dot from './dot.js';
 import Vector3 from './Vector3.js';
-import Matrix3 from './Matrix3.js';
+import Matrix4 from './Matrix4.js';
 
 class Bounds3 {
 
@@ -511,9 +511,8 @@ class Bounds3 {
    *
    * This is the immutable form of the function transform(). This will return a new bounds, and will not modify
    * this bounds.
-   * // TODO: Should be Matrix4 type, https://github.com/phetsims/dot/issues/125
    */
-  public transformed( matrix: Matrix3 ): Bounds3 {
+  public transformed( matrix: Matrix4 ): Bounds3 {
     return this.copy().transform( matrix );
   }
 
@@ -874,9 +873,8 @@ class Bounds3 {
    *
    * This is the mutable form of the function transformed(). This will mutate (change) this bounds, in addition to returning
    * this bounds itself.
-   * // TODO: should be Matrix4 type, https://github.com/phetsims/dot/issues/125
    */
-  public transform( matrix: Matrix3 ): Bounds3 {
+  public transform( matrix: Matrix4 ): Bounds3 {
     // do nothing
     if ( this.isEmpty() ) {
       return this;
@@ -907,14 +905,14 @@ class Bounds3 {
       maxZ = Math.max( maxZ, vector.z );
     }
 
-    withIt( matrix.multiplyVector3( vector.setXYZ( this.minX, this.minY, this.minZ ) ) );
-    withIt( matrix.multiplyVector3( vector.setXYZ( this.minX, this.maxY, this.minZ ) ) );
-    withIt( matrix.multiplyVector3( vector.setXYZ( this.maxX, this.minY, this.minZ ) ) );
-    withIt( matrix.multiplyVector3( vector.setXYZ( this.maxX, this.maxY, this.minZ ) ) );
-    withIt( matrix.multiplyVector3( vector.setXYZ( this.minX, this.minY, this.maxZ ) ) );
-    withIt( matrix.multiplyVector3( vector.setXYZ( this.minX, this.maxY, this.maxZ ) ) );
-    withIt( matrix.multiplyVector3( vector.setXYZ( this.maxX, this.minY, this.maxZ ) ) );
-    withIt( matrix.multiplyVector3( vector.setXYZ( this.maxX, this.maxY, this.maxZ ) ) );
+    withIt( matrix.timesVector3( vector.setXYZ( this.minX, this.minY, this.minZ ) ) );
+    withIt( matrix.timesVector3( vector.setXYZ( this.minX, this.maxY, this.minZ ) ) );
+    withIt( matrix.timesVector3( vector.setXYZ( this.maxX, this.minY, this.minZ ) ) );
+    withIt( matrix.timesVector3( vector.setXYZ( this.maxX, this.maxY, this.minZ ) ) );
+    withIt( matrix.timesVector3( vector.setXYZ( this.minX, this.minY, this.maxZ ) ) );
+    withIt( matrix.timesVector3( vector.setXYZ( this.minX, this.maxY, this.maxZ ) ) );
+    withIt( matrix.timesVector3( vector.setXYZ( this.maxX, this.minY, this.maxZ ) ) );
+    withIt( matrix.timesVector3( vector.setXYZ( this.maxX, this.maxY, this.maxZ ) ) );
     return this.setMinMax( minX, minY, minZ, maxX, maxY, maxZ );
   }
 
diff --git a/js/Matrix4.js b/js/Matrix4.js
index e3e1865..c4bac1f 100644
--- a/js/Matrix4.js
+++ b/js/Matrix4.js
@@ -304,6 +304,16 @@ class Matrix4 {
     return this.entries[ 15 ];
   }
 
+  /**
+   * Returns whether this matrix is an identity matrix.
+   * @public
+   *
+   * @returns {boolean}
+   */
+  isIdentity() {
+    return this.type === Types.IDENTITY || this.equals( Matrix4.IDENTITY );
+  }
+
   /**
    * Returns whether all of this matrix's entries are finite (non-infinite and non-NaN).
    * @public