I naively tried to calculate in a closed system consisting of cotton canvas but I got a temperature rise of 600K. Oh well, I guess heat loss from the system is

I naively tried to calculate in a closed system consisting of cotton canvas but I got a temperature rise of 600K. Oh well, I guess heat loss from the system is important. 600 W/m2 / (1.34 kJ/(kg K) * 390 g/m2) * 600s