What is a .usdz file?

What USDZ is for

USDZ is a package format for Universal Scene Description, the scene system Pixar built and open-sourced, now governed by the Alliance for OpenUSD.

The reason it matters outside film production is Apple. Since iOS 12, tapping a USDZ file on an iPhone or iPad opens AR Quick Look: the model appears in the camera view, scaled to real-world size, placed on a surface, and you can walk around it. There is no app to install. It works straight from a web page, an email or a message.

For anyone making a physical product, that is useful. Sending a client a USDZ of a bracket means they can put it on their desk at actual size before it is machined.

What is inside

A .usdz is an uncompressed zip archive holding a USD stage plus its textures. The format imposes two constraints, both because the runtime memory-maps the archive rather than unpacking it:

• Every entry is stored, never deflated
• The first entry's data begins on a 64-byte boundary

That is why a USDZ made with an ordinary zip tool usually fails to open, and why Apple ships a usdzip utility.

The stage inside comes in two flavours: USDA, which is text, and USDC, a binary crate format. Most exporters write USDC because it is much smaller. This site reads the text form and tells you when it finds the binary one, which is the same boundary other browser-based tools draw.

Units

USD stores metersPerUnit in the stage. The default is 1, so USD is metres unless the file says otherwise, and unlike glTF it *can* say otherwise. An exporter targeting AR Quick Look should set it correctly, because the whole point is that the model appears at true size.

If your USDZ appears comically large or small in AR, metersPerUnit is the first thing to check.

What USD stores

• A real scene hierarchy with transforms
• Geometry as meshes, plus NURBS and subdivision surfaces
• Materials through UsdPreviewSurface, which maps onto the same PBR model glTF

uses

• Animation, cameras, lights
• Layers and composition, USD's distinguishing feature, letting several

files be composed non-destructively. Little of this survives into a flattened USDZ.

What it does not

No exact CAD geometry, no parametric history, no tolerances. USDZ is a display format.

Making a USDZ

• Reality Composer and Apple's usdzip, on macOS
• Blender, which exports USD directly
• Fusion 360, Rhino and SketchUp via export or plugin
• Converting from GLB, which is the most common route and what this site does

AR Quick Look, practically

Serve the file over HTTPS with the MIME type model/vnd.usdz+zip, and link to it with rel="ar". Safari on iOS handles the rest. Android uses GLB with Scene Viewer instead, so a product page that wants AR everywhere ships both.