According to the post:
The iPhone 6 concept takes mobile innovation to the next level by combining aluminum with carbon-fiber to create a seamless unibody enclosure that increases strength while decreasing weight. Carbon fiber alone is perfectly rigid and doesn’t bend. Because of this, any hard impact will cause it to shatter. Aluminum is not as rigid as carbon fiber but does provide some flexibility as it can bend without breaking. By creating an aluminum-carbon fiber comosite hybrid enclosure, the iPhone 6 earns a 40% weight reducton and 60% strength increase. It wil not shatter when dropped or dent..