If a window is a glass sheet holding flat content, a volume is a transparent box holding content that has real depth. Users can walk around the 3D model inside, or grab and rotate it, and read it like a physical object. It's used for product mockups, characters, and terrain models.
The defining trait is a clear boundary — width, depth, and height. Content that crosses that boundary gets clipped, so it has to be scaled to fit inside. The boundary itself is usually invisible, showing only a faint outline when the volume is selected.
The demo spins a 3D object slowly inside a dashed bounding box — seeing a different face from every angle is the key difference from a window, which always shows the same flat front.
When to use
Reach for this only when the content genuinely benefits from being 3D. Don’t force inherently flat UI — buttons, text — into a volume.