"We were seeking to express the purity of glass blowing in this simple diamond shape," explained the designers.
"Glass is a material that likes round shapes. By developing the strict shape we are reaching the limits of the material."
Each vessel takes seven craftsmen 24 hours to produce at Iittala's glass factory in Finland, where the iconic collection of curvaceous vases by Modernist designer Alvar Aalto is also produced.
The Bouroullec's designs come in five sizes and seven watercolour tones, which can be fitted together in different arrangements to overlay the colours.
"Ruutu allows a game of composition," said the duo. "We wanted to show the sophisticated range of Iittala colours while at the same time handing the job over to the user who will feel tempted to have several modules to create his or her own individual assemblage."
Each Ruutu vase has the designers' names engraved on the base.
Ronan and Erwan Bouroullec have also used coloured glass to create a furniture collection for Glas Italia, presented in Milan earlier this year.