This week's collection of space savers includes items notable not only for their economy but also for their ability to perform a big reveal. Like a micro-apartment that brilliantly transforms to suit a certain household occasion, these items shift, fold and squinch in one state and then stretch out, unfurl and pop open in another. Overall, the accordion effect is delightful.

Beyond removing table leaves and unfolding a sofa bed, our big household purchases typically resist adaptation. But the Austrian-born, London-based designer Stephanie Hornig suggests, with her Set expanding shelving unit, that more flexibility should be baked into our furniture. Her powder-coated steel and beech bookcase can rest in three widths that, like a child-proof gate, will adapt to the parameters of a space.

Kites often fold up for storage and transportation, but Prism Designs' line of EO (Expandable Object) kites do so with particular flair. Designed by the Australia-based kite maker Phil McConnachie, who has been constructing tethered fliers since he was 12, the EO series may not appear out of the ordinary when transported flat. But when McConnachie's designs are ready to fly, they pop up into elaborate 3-D constructions. The EO-6, for instance, unfolds into an open cube that kind of resembles a giant airborne waffle fry.

Collapsibility can also be good for the environment. UltrAspire's six-ounce polyurethane satchel is made to cut the waste accrued during group runs. If 5K participants sip from and then crumple three plastic cups per race, just imagine how much trash piles up when thousands of racers cover longer distances. With conservation at its core, the UA cup folds up tiny enough to fit into body-hugging, sweat-wicking runners' pockets before and after unfurling to full size for a fill-up at water stations. A loop on one end helps the cup steady on the athlete's hand and will attach to a clip or carabiner with ease.

A helmet isn't an object that you typically want to collapse on you; it's supposed to crumple to save our noggins on impact, but never before. And yet cyclists would be more likely to carry helmets if there was some way to make them less bulky—and this summer has seen two proposals for just such a design. Over on Coroflot, Michael Rose, a UK-based industrial designer, published a helmet prototype that's meant to compress to nearly half its size when you're lugging it around—but will, he says, maintain its head-cushioning properties when worn. On the sides, it's normal helmet fare: expanded polystyrene pads capped by an outer shell. But in the center is something different: polypropylene origami that will contract when pushed from the sides, but stands up to impacts when struck directly.

See more project details on Coroflot

A Kickstarter proposal by the Spanish studio Closca takes a different approach. It uses a telescopic design with three layers of EPP foam joined by cross straps. Not only can the Closca Helmet be stowed flat, reducing its volume by 50 percent, but it comes wrapped in one of a variety of covers that resemble oversize newsboy caps—more stylish, at least, than your typical hunk of Styrofoam.