They’re carbon negative and stronger and lighter than wood according to their creator, US start-up Plantd. Machines in its North Carolina factory strip fibres from fast-growing grass and turn them into panels that can be used for walls, roofs and flooring. The grass grows up to 9 metres a year. It absorbs more CO2 than the same volume of trees and while a farmed pine can take 15 years to reach maturity and can be harvested 3 times in a single growing season