Nowadays, sustainable construction is a key factor for reaching net-zero emissions of carbon dioxide all over the world. This goal is impossible to achieve by merely reducing the energy consumption of end-users. A more holistic approach should be taken, adopting sustainable industrial practices that use environmentally friendly materials on a large scale. This paper presents the analysis of the hydrothermal properties of hemp thermal insulation plates. We carried out extensive measurements and the analysis of the thermal conductivity coefficient, drying-out dynamics, and water absorption. The study was performed with experimental insulation samples based on the fiber obtained from hemp stems, prepared using different adhesive powders. The dimensions of the analyzed samples were 300 × 300 mm. The proposed samples are not yet available in mass production. Hemp does not flower in the Baltic region and was traditionally used for soil regeneration. Thus, using this raw material increases the added value of agricultural residues. Three series of hemp fiber samples with different substances and pressing modes were evaluated in the study. Each set of samples consisted of four plates with varying thicknesses and two different densities: 200 kg/m3 and 300 kg/m3. All samples exhibited a significant increase in moisture absorption and a strong correlation with the increase in thermal conductivity. The average thermal conductivity of the test samples ranged from 0.0544 to 0.0594 W/mK. The impact of the adhesive powder on the thermal conductivity was found to be extremely small. However, the values obtained were much higher than those for traditional thermal insulation materials, allowing to utilize the local agriculture residues and providing material for the construction of eco-friendly buildings.