While everyone's attention is on the likes of Oculus Rift - due in 2016 - Sony's Morpheus, it's Google Cardboard that's quietly stealing VR mindshare.

A year on from the introduction of the simple open source phone VR mount, Google has announced that over 1 million Google Cardboards have been sold.

That's double the 500,000 figure announced in December.

Growing audience

The reason this is interesting is that Google doesn't sell Cardboard itself; instead a range of thirdparty vendors offer the basic design in a variety of materials, colours and themes.

In order to tighten up on standardisation, Google recently announced a new SDK and its Cardboard certification program, which enables vendors to demonstrate their version is fully compatible, also giving consumers confidence that the $20+ price is good value.

Alternatively, people can download the design template and build their own - assuming they can source the lens and magnetic button components.

At Google I/O 2015, attendees got the new version of Cardboard, which sports a simplified design and now support 6-inch devices and iPhones.

Of course, no one's saying that Cardboard can technically compete with the Oculus Rift, but the audience of VR early adopters could give Google a strong headstart if it - or another partner - wanted to use the Cardboard ecosystem as the launchpad for a more serious contender.