Design duo Foersom & Hiort-Lorenzen has worked with furniture brand Norman Copenhagen on a collection of plant-based chairs, unveiled today as part of Stockholm Design Week.

The Mat collection features two chairs; one is made from hemp – a type of cannabis plant, and the other combines this material with eelgrass, a marine plant similar to seaweed.

These biomaterials were used instead of injection-moulded plastic to create a shell chair, which sits on powder-coated steel legs.

On show at Norman Copenhagen's showroom throughout Stockholm Design Week, the Mat chairs mark the brand's first foray into the world of bio-based plastics.

Jan Andersen, co-founder and CEO, said it forms part of "a commitment to explore new, innovative production methods".

"When Foersom & Hiort-Lorenzen approached us with their hemp chair project, we were immediately curious," he said.

The design has been decades in the making.

Peter Hiort-Lorenzen, co-founder of Copenhagen-based Foersom & Hiort-Lorenzen, first became interested in using plant fibres as a substitute for plastic in furniture in the late 1990s.

The studio presented its first chair prototypes in 2005, but it wasn't until 2008 that it started trialling the use of hemp.

"Now, some 20 years later, the hemp material we have developed in collaboration with Normann Copenhagen is more responsible, a lot sturdier and with a higher aesthetic appeal than any of the previous prototypes," Hiort-Lorenzen said.

"It's a one-of-its-kind product."

The Mat chairs were developed in collaboration with hemp specialists from the Danish Technological Institute.

The shells were produced from hemp stems rather than leaves, which already have other applications in food and textile production. These stems are sourced from farms that typically treat this part of the plant as a waste product.

For the eelgrass chair, the hemp fibres ware combined with dried eelgrass, collected after it washes up on the Danish coast.

The production involves turning the milled hemp and eelgrass fibres into a sheet material. These are then shaped, using a specially developed compression machine, and cut.

To produce the sheet material, the fibres were mixed with a "bico binder". This was chosen over a bio-based binder to make the chairs easier to recycle at the end of their lifecycle.

"The idea of using a bio-based binder is appealing since it's a natural material and would reduce the use of oil," said Søren Stryhn Petersen, chief technology officer at Normann Copenhagen.

"However, since the beginning of this project, it has been very important for us that the material we use can be recycled," he told Dezeen.

The different fibre mixes offer different colours. The hemp chair has a warm, light tone similar to oak, while the eelgrass chair has a muted brown shade.

The material is hand-sanded for a smooth finish and finished in a VOC- free linseed oil.

Both the design and the production process support a zero-waste approach. Manufacturing offcuts can be reused to make new sheet material, as can old chairs that are beyond repair.

The Mat collection is not the only example of bio-based chairs on the market. Fellow Danish brand Mater makes shell chairs from coffee grounds, while design office Prowl Studio recently presented an injection-moulded chair that combines hemp with corn-derived PLA.

Normann Copenhagen hopes to explore more biomaterial products in the future, although the brand is mindful of the investment required to do so.

"Due to the lack of prior know-how, it requires a lot of resources to create something innovative like this," said Stryhn Petersen.

"For now, we are looking into other projects where the same material composition can be used, and at other ways to use the production waste."

Mat is available as a dining chair or barstool, either with or without upholstery.

Mat is on show from 5 to 8 February at Norman Copenhagen showroom at Katarina Bangata 26, Stockholm. See Dezeen Events Guide's Stockholm Design Week 2024 guide for information about exhibitions and events taking place throughout the week.