A third-world dimension

EVERY summer, Seattle holds a raft race in Green Lake, a park that is the eponymous home of the water the rafts must cross. Entries for the Milk Carton Derby have to be made from old plastic milk bottles. The result is a wonderfully Heath-Robinson collection of improvised craft. But this year one stood out: the entry from the University of Washington’s engineering department actually looked like a boat. The students who built it, Matthew Rogge, Bethany Weeks and Brandon Bowman, had shredded and melted their bottles, and then used a 3D printer to print themselves a plastic vessel.

No doubt the Milk-Carton-Derby rules will be tightened next year—though in the end, the team came only second. But they did come first in a competition that mattered more. On October 19th they won $100,000 in the 3D4D Challenge, organised by a charity called techfortrade.