The paper presents preliminary results of research on lightweight composite based on building gypsum. In order to improve the insulating properties of gypsum plasters, researchers often use various additives with thermal insulation properties, primarily aimed at enhancing the thermal performance of such gypsum composites. Examples include expanded cork granules or polystyrene granules. In this study, we decided to explore a different mechanism to increase the porosity of the composite without using such additives. For this purpose, we utilized the phenomenon of starch gelatinization directly in the fresh gypsum slurry. As a result, a material with very high porosity is obtained. The resulting composites exhibit porosity ranging from 60% to 90%, which significantly enhances their thermal insulation properties. We prepared a total of six types of mixtures, starting with a reference composition without starch, where the water-to-gypsum (W/G) ratio was 0.6. In each subsequent formulation, the amount of gypsum was reduced, allowing for the production of a final material with lower density. The fundamental properties of the gypsum composites obtained through this process were determined, including density in a dry state, thermal properties and compressive strength. The sorption properties of the materials were also examined using the dynamic water vapor sorption (DVS) method. This analysis provided sorption and desorption curves for composites of varying densities. Additionally, preliminary qualitative tests of the microstructure were conducted using an scanning electron microscope. The solution presented in this paper offers the advantage of producing a gypsum-based material with high porosity (>60%). Utilizing the starch gelatinization process directly within the slurry allows for the creation of a highly homogeneous material. In this process, the initial, temporary structure is formed by the starch gel, which serves as a framework around which the final gypsum-based structure develops after the gypsum’s setting time is reached. The innovativeness of the tested material concerns a group of materials with very good thermal properties, with the use of an easily available, relatively cheap admixture in the form of starch. It can be used for the production of e.g. lightweight plasterboards, internal thermal insulation, blocks and partition wall panels. Due to its lightness and the possibility of incorporating natural-based additives such as starch, gypsum composites align with the concept of sustainable construction, reducing resource consumption and CO₂ emissions.