Movie: in this exclusive video filmed at the unveiling of the 15th Serpentine Gallery Pavilion, architects José Selgas and Lucía Cano explain how their structure plays with coloured, translucent and mirrored plastic sheet.

SalgasCano's pavilion, which opens to the public later this week, consists of two layers of coloured ETFE (Ethylene Tetrafluoroethylene) plastic wrapped around a white steel frame.

"The whole pavilion for us was a kind of experiment," says Selgas in the movie. "We wanted to test different things with a new material, in this case ETFE. We wanted to try out [how the material could create] different shadows, colours and effects, which we haven't tested before."

Some parts of SelgasCano's structure are covered with large sheets of coloured ETFE, while other areas feature strips of the material wrapped around the steel frame. The Madrid-based architects also chose to vary the opacity of the material across the skin of the pavilion.

"We decided to play with the ETFE in many ways," Selgas says. "We created different effects by exploring what the possibilities are when you keep the transparency, or if you add different mirror effects."

The layers of coloured plastic cast multicoloured patterns across the floor of the pavilion when the sun shines.

"The most important colour for us is the colour of the floor," Selgas says. "It was very important for it to be white to get all the effects from the roof."

The structure consists of four arms, which branch off from a central area housing a bar and meeting space. Selgas says this form evolved organically as the architects experimented with how the ETFE sheets could be stretched across the steel frame.

"People ask us why we chose this shape," Selgas says. "But the shape comes from trying to stretch the material as much as possible."

There are multiple entrances and exits to the pavilion and no prescribed route through the structure. Selgas says he is keen to see how people use the space.

"The experiment is also very much related to the people that are going to visit the pavilion," he says. "We want them to decide how to interpret the pavilion, how they want to move around. It's very free in that way."

The 2015 Serpentine Pavilion will open on 25 June and close on 18 October. It will host a number of parties and public talks, as well as a series of evening events sponsored by fashion brand COS.

To mark the 15th anniversary of the pavilion programme, Dezeen will be publishing a series of exclusive interviews with director Julia Peyton-Jones, looking back at each of the designs. In the first movie in the series, Peyton-Jones compares SelgasCano's use of coloured plastic to stained glass.

This movie was filmed by Dezeen at the Serpentine Gallery in Kensington Gardens, London. Photography is by Jim Stephenson, unless otherwise stated.