Energy consumption in the residential sector and air pollution are relevant topics for the global population. One of the causes, especially in cold climate cities, is that buildings maintain a high energy consumption for heating and cooling, primarily using low-efficiency biomass combustion for heating, which releases a significant amount of particulate matter into the environment. In this context, thermal insulation materials play a crucial role in reducing the energy demand of buildings, requiring advancements in the sustainable development of such materials within the context of climate change. This study carried out an evaluation of two algae species found along the Chilean coasts, with the aim of characterizing them and creating a prototype of a sustainable material. Their physicochemical properties were analyzed, and the results demonstrate that the algae exhibit excellent thermal insulation properties, with an average thermal conductivity of 0.036 [W/mK]. This result is comparable to expanded polystyrene (EPS), a widely used material in the Chilean and global markets, which has an average thermal conductivity value of 0.038 [W/mK]. Additionally, the algae show a good thermal stability, and their morphology contributes to the development of a bulk material, as they possess a porous structure with air chambers between the fibers. © 2023 by the authors.