You've probably seen the gross phenomenon where someone takes a bite out of something, and as they pull the food away from their face, a long spit-bridge is temporarily stretched between their mouth and the food.
Something like this happens in FDM 3D printing, too; let's say you're printing two separate pieces with space between them on the bed, and as the nozzle moves from one piece to the other, an unwanted string of material leaks out of the nozzle and is stretched across the bed.
Jack Forman of MIT Media Lab's Tangible Media group saw that unwanted string as an opportunity. First off, he explains how not to create that unwanted string: "In order to yield successful prints, the speed of the nozzle head, and the amount of material extruded must be carefully coordinated to yield uniform layers," he writes. "The most common parameter used to fine-tune the amount of material extruded is the extrusion multiplier (EM)."
What if you exploited the EM to purposely create the string in a carefully controlled way? Then you could do stuff like this:
What Forman is doing is printing in a form that emulates the warp and weft of fabric:
And by controlling the warp and weft, an entirely new world of 3D-printable possibilities opens up. These have to be seen to be believed:
The skirt that you print small and expand, the interactive lampshade, the deformable shuttlecock, the freaking 70-meter-long sheet printed in one go--it's amazing to think Forman could create all of these just by encoding small gaps into the print. Best of all, he did it "using an inexpensive, unmodified, 3D printer with no additional software."
Forman calls the technique "underextruding" and refers to the resultant creatiosn as "DefeXtiles." You can learn more about the technique and its possibilities here.