With the increasing focus from policymakers to a circular economy, assessing the environmental impacts of circular products is becoming more important. In this thesis a Life Cycle Assessment of the new circular composite Re-plex is performed. The Re-plex can be used as building material. Re-plex is produced from Kaumera Nereda® Gum recovered from Nereda® wastewater sludge, and Recell® cellulose recovered from wastewater. Re-plex is still in the developmental phase, this LCA is performed to aid engineers to reduce the environmental impacts of the Re-plex composite. A comparative LCA is performed in which the current Re-plex production is compared to Fire-retardant Medium Density Fibreboard (FR-MDF) with the ILCD impact assessment family. The functional unit is 1 year of 1m2 use of interior finishing material. The Re-plex has a better characterisation result in the impact category; Human Health (HH), respiratory effects, inorganics. The FR-MDF has better characterisation results in the impact categories; Climate change; Ecosystem Quality (EQ), acidification; EQ, freshwater ecotoxicity; EQ, freshwater eutrophication; EQ ionizing radiation; EQ, marine eutrophication; EQ, marine eutrophication; Human Health (HH), carcinogenic effects; HH, ionizing radiation; HH, non-carcinogenic effects; HH, ozone layer depletion; HH, photochemical ozone creation; Resources (RS), land use; and RS, mineral, fossils and renewables. Scenarios are developed to improve the environmental performance of the Re-plex production. Increasing the amount of cellulose in Re-plex does not seem to improve the environmental performance. Three scenarios do improve the environmental performance; Replacing citric acid by succinic acid; improving the energy efficiency; and drying the Kaumera Gum before transport. These three improvements are combined in the new Re-plex scenario. The improved scenario has better characterisation results than FR-MDF in the ten impact categories; Climate change; EQ, acidification; EQ, freshwater ecotoxicity; EQ, freshwater eutrophication; EQ, marine eutrophication; EQ, marine eutrophication; HH, carcinogenic effects; HH, non-carcinogenic effects; HH, photochemical ozone creation; and HH, respiratory effects, inorganics. FR-MDF scores better in the five impact categories; EQ ionizing radiation; HH, ionizing radiation; HH, ozone layer depletion; RS, land use; and RS, mineral, fossils and renewables. Engineers working on Re-plex are advised to change the use of citric acid to a better environmentally performing material. The environmental benefit of changing this material will add more value to a Re-plex product than the lower price when using citric acid. Further, the focus should be on improving the energy efficiency of Re-plex production and realising a lifetime of Re-plex of 32 years, similar to MDF. If these improvements can be realised, Re-plex has a better environmental performance than FR-MDF.