Breathing under snow, e.g. while buried by a snow avalanche, is possible in the presence of an air pocket, but limited in time as hypoxia and hypercapnia rapidly develop. It was suspected that the snow physical properties affect the development of hypoxia and hypercapnia. The aim of this study was to evaluate the influence of different snow physical properties on the development of hypoxia and hypercapnia in subjects breathing into an artificial air pocket in snow. Twelve male healthy subjects breathed through an airtight face-mask and 40cm tube into an artificial air pocket of 4L. Every subject performed three tests on different days with varying snow characteristics. Symptoms, gas and cardiovascular parameters were monitored up to 30min. Tests were interrupted at SpO₂<75% or hypercapnia (i.e. FiCO₂ >8%) or due to discomfort. Snow density was assessed via standard methods. In eighteen of 36 (50%) tests, subjects completed the full test duration of 30min; tests were terminated due to hypoxemia (SpO₂≤75%) in 13 (36%) cases and due to clinical symptoms in five (14%) cases. Changes of O₂ and CO₂ in the air pocket were correlated with snow density (p<0.05), but not with permeability and other related measurements. A rapid decline in O₂ and increase in CO₂ were mainly associated with higher snow densities and led to premature interruption due to critical hypoxia (SpO₂≤75%). In the low snow density setting a higher frequency of test interruptions than expected occurred, which was linked to clinical symptoms and rapid CO₂ accumulation in the air pocket. In conclusion, snow density seems to have a direct influence on the respiratory gas concentrations and thus test duration of subjects breath· ing into an artificial air pocket.