If you were attending the Salone del Mobile in Milan this this week, you might have seen a little black Daihatsu pickup driving around with some nebulous cargo in the back—the Cumulus Parasol, a cloud-like umbrella that inflates in reaction to sunlight.

Cumulus is the work of the Netherlands-based Castor Bours and Wouter Widdershoven. The duo has been working together on explorative design projects since early 2007, forming Studio Toer in the center of Eindhoven in 2011. "When you look around, most interiors are static," Bours says. "We want to create products that communicate with you. The Cumulus Parasol was developed from an exploration in creating an object that reacts to its own surroundings."

It works via four small, rectangular polycrystalline solar cells that harvest energy from the sun. The polycrystalline cells are made up of raw silicon, melted and poured into a square mold, that is cooled and cut into perfectly square pieces. As one of the most standardized processes for making solar panels, polycrystalline panels tend to be the least expensive on the market and can be easily sourced online, as was the case for Studio Toer. One slight hitch: Even though the polycrystalline panels are low in intensity, the duo found that too much power allowed the parasol to inflate in no sun. "Which is no fun," says Castor.

Studio Toer remedied this by using fewer and smaller solar cells that only kept the parasol inflated for as long as it's in direct sunlight. When charged, the panels transfer energy to a 12-volt ventilator positioned at the roof of the umbrella. The ventilator is sewn into the top of the nylon body, and when on, it inflates the Cumulus Parasol in 20 seconds. When the sun is obscured, the parasol automatically deflates. For manual control, there is also a power switch integrated into the pole.

The solar cells and fan on top of the parasol

Cumulus in action in Milan

With no core structure, the parasol gets its form (and, clearly, its name) from the nylon body that inflates via the fan. In initial experiments, Castor and Widdershoven began with an old tent, inflating it with a fan to test the idea. Satisfied with those tests, they moved on to nylon and Tyvek and began pattern-making. "We started with making the real-size parasol from plastic foil—two circles on top of each other, just stuck together with transparent tape," Bours says. "To define where the connections should be, we used magnets. You can easily position them and see what it does with the shape."

Through trial and error, the designers were able to manipulate the parasol's shape to create the ideal mass of cumulus. They borrowed a sewing machine from Bours's girlfriend to sew together the final prototype, using a type of nylon pre-coated in silicon to make it waterproof. "I don't know if we found the perfect measurements," Bours admits. "But it's big enough to be called a parasol." Indeed, with a diameter of two meters in length, Cumulus is wide enough to provide shade for a small group.

While the one working prototype of the Cumulus Parasol is currently driving around Milan, it is also available for pre-order on Studio Toer's website for 465 euros, or roughly $640.