## 1 Introduction  
Wood has long been used by humans for diverse purposes, including housing, musical instruments, furniture, and fuel. Recently, it has gained renewed attention as a key material for building a sustainable society. This is because wood can store carbon and, when used as a construction material, generally has lower environmental impacts such as energy consumption and carbon emissions compared to other materials [1]. Recognizing these advantages, many countries including Canada, Finland, Sweden, Japan, China, and the United States have adopted wood as a primary material in construction [2].  
Concurrently, contemporary architectural trends have moved toward an integrative approach that considers the psychological, physical, and behavioral needs of the occupants [3; 4; 5]. Therefore, to facilitate the development of wooden environments that align with the occupants' needs, it is essential that we expand the research on the impacts of wooden interiors on human health and well-being, as well as the associated factors, across a range of environmental conditions. Recent field-based investigations have begun to address this need. [PERSON] et al. compared two full office rooms, one with pine wood surfaces and another with conventional materials. In a crossover test with 61 participants, the wooden room was perceived as more pleasant and natural, with low VOC emissions. These finding show that wooden interiors can improve indoor environmental quality and occupant perceptions [6].  
In South Korea, various policies are being supported to expand the use of wood to achieve the 2050 carbon neutrality goal. However, there is relatively little research verifying the impact of the actual wooden environment on humans' physiological well-being. This study aimed to analyze how constructing indoor spaces with wood and varying the degree (0%, 45%, and 90%) of wood coverage would affect the physicochemical properties of the indoor environment and the physical responses of occupants. The _Larix kaempfer_ used as the interior finishing material is considered one of the most economically valuable domestic tree species and is currently a key material in the South Korea timber industry [7].  
RH (relative humidity) and IAQ (indoor air quality) were measured to characterize the physicochemical alterations associated with wooden indoor environments. The humidity regulation and function of wood in indoor environments have been reported to influence occupants' thermal and respiratory comport [8]. Wood in service is exposed to both long-term (seasonal) and short-term (daily) changes in the relative humidity and temperature of the surrounding air, which induce changes in the wood moisture content [9]. A series of experiments were conducted in real indoor environments using various ventilation rates, hygroscopic-material-loading rates, and moisture loads to investigate the moisture buffering effects of three types of hygroscopic materials, including wood [10]. [PERSON] et al. reported that the use of hydrogen materials, such as wood, increases residents' thermal comfort by approximately 10% and enhances air quality satisfaction by 25%, ultimately improving overall health satisfaction [11]. Several studies have investigated the moisture-buffering capacity of _L. kaempfer_ as interior materials [12], as well as the water sorption characteristic related to anatomical differences such as earlywood and latewood [13]. However, quantitative evaluations of the optimal composition ratios are required for actual indoor applications and their effects on occupants' physiological responses. The physiological responses of the participants were indirectly assessed by examining autonomic nervous system activity based on changes in HRV, thereby indicating the level of physical relaxation.