The other type of non-military headgear seen on Mao badges is the "hard-hat" made from woven strips of bamboo. The natural resilience of bamboo provided equivalent protection to aluminium or plastic, but with better ventilation. These hard-hats were widely worn by miners, forestry workers, and some construction workers.
PLA miners wearing bamboo hard-hats:
illustrations from a 1968 lianhuanhua entitled (approximately) The Victory Song of the Selfless Character