Today, long-distance driving and prolonged sitting in offices are increasingly common, making seat comfort paramount. The comfort of seating systems—such as automotive seats, office chairs, or upholstered furniture—is influenced by various ergonomic attributes, with thermophysiological comfort being a critical factor.
Thermophysiological comfort in seating systems can be characterized using the Hohenstein skin model (sweating hot plate), compliant with ISO 11092. This model determines specific thermophysiological quantities of textiles as surface layers. Under steady-state conditions, water vapor resistance (Ret) is measured to represent insensible perspiration. Higher sweating rates (sensible perspiration) are evaluated using water vapor buffering capacity (Fd) and liquid sweat buffering capacity (Kf). Further refinement involves simulating seated individuals using a sweating buttock model or a thermal, sweating manikin like Thermetrics' Newton. Integrating humidity sensors within seats enables the assessment of moisture management capabilities.
Contact area and pressure distribution between the human body and seats are also vital for ergonomic comfort. Pressure mapping pads quantify seated pressure distribution, while 3D scanning systems (e.g., Artec Eva, Creaform Revscan, or Kinect) capture seat geometry for comparison with target population data, identifying contact region sizes and shapes.
Comfort lacks a universal definition; physiologically, it is a multidimensional concept influenced by physical, physiological, psychological, and environmental factors. One perspective defines comfort as the absence of discomfort. Seated comfort is particularly significant given extended daily sitting durations, averaging 7.5 hours. Comfort evaluation should encompass sensory, thermophysiological, and ergonomic dimensions.
Methods and Discussion
1 Sensory Comfort Characteristics
Sensory comfort is primarily determined by textile surface properties. The "wet cling" index (iK) quantifies unpleasant skin adhesion using a specialized sintered glass plate instrument. Lower iK values (ideally below 15) indicate less discomfort. Textile moisture absorption speed, assessed via contact angle and absorption time (iB, ideally below 270), impacts skin sensation. Surface roughness, measured by fiber end protrusion density (surface index io), should range between 3–15 for optimal comfort. Smaller contact areas (nK, ideally below 1500), determined by 3D imaging, reduce tackiness. Fabric stiffness (s), measured by bending angle (0–90 scale), should be 5–27 for athletic wear.
2 Thermophysiological Comfort Characteristics
The Hohenstein skin model simulates dry and sweating skin, measuring water vapor resistance (Ret), short-term water vapor absorption (Fi), and thermal insulation (Rct) per ISO 11092. Lower Ret and higher Fi indicate superior performance. Buffering capacity is differentiated into:
- Water vapor buffering (Fd): Evaporation within sweat pores before liquid formation.
- Liquid sweat buffering (Kf): Management of visible perspiration.
Non-steady-state conditions are simulated using protocols like BPI 1.2, with Fd and Kf values informing performance under high-sweat scenarios (e.g., prolonged driving).
Sweating Buttock Model
A 400N-loaded sweating buttock model (Thermetrics) simulates adult males, measuring microclimate temperature/humidity via integrated sensors. Initial heat flux (Hci) indicates cold/hot seat perception, with Hci max <85 W/m² for acceptable comfort and <64 W/m² for optimal comfort. Rapid skin-seat temperature alignment is desirable.
Thermal Sweating Manikin
Developed since the 1980s, manikins like Thermetrics' Newton (20–35 segments) and Andy enable whole-body thermal (Rc) and vapor (Re) resistance measurements under non-isothermal and isothermal conditions, respectively. ASTM F2370 standardizes Re measurements, with ongoing ISO standardization efforts. Computational models (parallel, series, global) yield divergent results, necessitating application-specific model selection.
3 Ergonomic Comfort Characteristics
Pressure mapping systems (e.g., Juqiao Seat Comfort V1) quantify seated pressure distribution, informing contact area and seat firmness evaluations. 3D scanning compares seat geometry with target population data, addressing questions like:
- Adequacy of seat dimensions (length, width, backrest height).
- Contact area size/shape.
- Accessibility and efficiency of adjustment controls.
Dynamic 4D scanning and demographic data aggregation enable the creation of "ideal" seat configurations and adaptive seating concepts.
Conclusion
Seating comfort is a multifaceted concept encompassing sensory, thermophysiological, and ergonomic dimensions. Thermal manikins and skin models provide critical insights into moisture and heat management, while pressure mapping and 3D scanning evaluate ergonomic performance. Integrating these methodologies enables comprehensive comfort assessment and optimization, enhancing user experience. Emerging technologies promise further advancements in addressing evolving comfort demands.
