A cow's udder stuffed with newspaper and wrapped in strips of masking tape might not sound like your average architectural model. But then Smiljan Radic, the Chilean designer chosen for this summer's Serpentine Gallery Pavilion, is no ordinary architect. This bandaged bladder, along with hollowed-out pebbles and torn papier-maché doughnuts, has fed in to the development of one of the strangest structures Kensington Gardens will have ever seen when it opens to the public on 26 June.

Looking like the result of an alien visitation to some ancient pagan site, the pavilion will take the form of a delicate white fibreglass cocoon, resting on a ring of boulders above a sunken grassy bowl, as if a mutant spider had spun a great nest on top of a neolithic stone circle.

"I want to bring back a sense of primitive space to the tradition of the folly in the park," said Radic, speaking from his studio in Santiago. "I like fragile constructions that have nothing to do with the history of architecture – like road-side fruit stalls, travelling circus tents and the simple shelters people build for themselves with whatever materials are to hand."

The 48-year-old, who is one of the youngest and least-known architects yet selected in the Serpentine's 14-year programme, has forged a reputation in South America for building structures of startling originality that play on their material counterpoints, combining natural and artificial, roughly hewn with smoothly polished. From luxurious villas that cling to the cliffs of the Chilean coast, to larger museum and civic centre projects, his work contrasts raw geological power with the delicacy of things that feel woven or grown. It is organic, but in way that is as awkward and brutish as it is sumptuous and refined. It is touchy feely – but you might get scratched.

Radic's extension to a charcoal burner's house in Culiprán is made out of the kiln itself, formed from a big ball of clay and straw that looked like the work of a dung beetle, then burnt out from the middle and chopped in half to form a craggy dome. His Mestizo restaurant in Santiago is composed of crisp black concrete beams resting on top of massive granite boulders, as if Mies van der Rohe had collaborated with the Flintstones.

'Like the result of an alien visitation to some ancient pagan site.' Photograph: Serpentine / Smiljan Radic

For the Serpentine, the torus-shaped fibreglass shell will appear like the cast-off chrysalis of some bulbous insect, ripped open where its maker wriggled out. In all cases, these are spaces to be experienced from within, not objects to look at from outside.

"I find contemporary architecture gives too much attention to the surface and the visual sense," said Radic. "I'm more interested in the ability of architecture to create an ambience, to give the air a certain quality, with noise, pasty light, suspended dust or an unusual temperature."

He represents a welcome direction in the Serpentine's choice of lesser-known, more thoughtful architects for this annual commission, after a decade of big-name "starchitects" produced mixed results – from Frank Gehry's clumsy pile of collapsing beams in 2008 to Jean Nouvel's tacky red boudoir in 2010. Last year's beguiling cloud of white steel rods, by the relatively obscure Japanese architect Sou Fujimoto, was one of the most visited pavilions yet.

"Radic is a key protagonist of an amazing architectural explosion in Chile," said Serpentine directors Julia Peyton-Jones and Hans Ulrich Obrist. "It's the Chilean miracle. In the same way that he makes such innovative use of available materials, his versatility as an architect enables him to respond to the demands of each setting."

"They are taking a big risk by choosing me," said Radic. "I'm not inside the common place of the architect, and it is really hard for me to do something so fast. But risks can be exciting."