The imperative to enhance traditional masonry walls in accordance to architectural heritage requirements has prompted the exploration of solutions for hygrothermal improvement. It is established that capillary-active insulation materials demonstrate efficacy in cold climates. Reed and wood fiber board both qualify as capillary-active materials. Different manufacturers have varying technical specifications for wood fiberboard, and in the case of reed board, there was no available data. Therefore, the technical specifications needed to be established or determined through testing. Diffusion resistance for wood-fibre board µ = 3,33 and reed board µ = 5,35 were measured and calculated, capillary absorption coefficient, and moisture absorption coefficient were conducted for both wood fiber board Aw = 0,0019 kg/(m2·s0,5) and reed board Aw = 0,0027 kg/(m2·s0,5) also sorption/desorption cures were generated. Subsequently, the hygrothermal properties of the test wall in Mooste Manor stable were assessed. The masonry wall, leveled with clay, incorporates interior insulation using wood fiber board and reed board. The entire wall was finalized with clay plaster. Reed board and wood fiber board exhibited capillary absorption properties and are suitable to use in this interior insulation system. Notably, the most vulnerable areas were identified near the floor due to the absence of foundation waterproofing and colder temperatures. Mold samples taken from the test wall were sent to laboratory and posed no health risks.