Floral walls versus green wall for stress recovery and cognitive restoration in underground environments: A VR-based experimental study

Underground environments without light wells or skylights lack a connection to the natural outdoors, heightening stress and mental fatigue, jeopardizing health and productivity. While green walls are established restorative agents, the contribution of floral colour to underground stress recovery remains unclear. Ninety-six adults completed baseline and stress-induction phases before immersive exposure—via virtual reality—to yellow-floral, white-floral, red-floral or green walls. Multi-modal assessment integrated self-reports, cardiovascular metrics and cognitive tasks. Relative to the stressor phase, all scenes reduced negative affect and elevated perceived restoration, with yellow-floral and red-floral walls additionally increasing positive affect above baseline. Red-floral wall uniquely maximised vagal reactivation (largest root mean square of successive differences gain, steepest stress-index decline), indicating superior autonomic recovery. Green wall expedited information processing, whereas yellow-floral wall optimised working-memory capacity. These findings elucidate colour-specific pathways by which floral stimuli mitigate underground stress and inform evidence-based chromatic interventions for subterranean design. • Underground floral walls' stress recovery and cognitive benefits were explored. • Red- and yellow-floral walls reduced stress and improved mood versus baseline. • Red-floral wall increased PNS activity, promoting human relaxation. • Green wall accelerated task processing in arithmetic and visual reaction tests. • Yellow-floral wall maximally enhanced memory span in the digit span (9.17 %).