Northmodern 2016: the natural dye used to colour this sleeping bag by Dutch studio Buro Belén slowly pales over time, allowing the pattern in the fabric to become more visible.

Laying Bag is the result of a collaboration between Buro Belén and Dutch interior fabrics studio Febrik.

For the natural dye to take to the fabric, the sleeping bag had to be constructed from all-natural materials, so the designers opted for merino wool.

"The Laying Bag matches smart production to the wonderful relief that makes Febrik textiles so unique," Buro Belén told Dezeen. "The Febrik machine weaves cylindrical fabrics, which can be cut open and used for upholstery and in other applications."

"However, we decided to use the machine as a kind of 3D printer that gives the product its shape as it produces the material," they added.

The studio – set up by designers Brecht Duijf and Lenneke Langenhuijsen – wanted to showcase the benefits of using natural dyes and coloured the material using pigment made from logwood.

"Plant dyes are not used by industries because they are afraid of their natural characteristics – mainly because they are unstable. We show what you can do with them if you collaborate with them," they said.

"The plant dyes decide the colour, and we collaborate with them," the duo continued. "We compose it into a tasteful palette that changes colour over time."

One variation of the Laying Bag changes from pink to soft yellow, while another turns from cool grey to beige.

The Laying Bags are among other naturally dyed products from Buro Belén's Spring Summer 2016 collection, including wallpaper coloured using red peppers and rugs dyed with rubia.

The whole collection is debuting at the Northmodern design fair in Copenhagen, which runs from 13 to 16 January 2016.

Other projects on show include laboratory-style vases by Danish studio Dubokk, and a collection of lamps featuring bendy LED lights arranged in loops by Studio Truly Truly.