Bamboo is the best fabric for your scalp during treatment.
I was initially drawn to it as a fabric as it is incredibly soft, personally I think that bamboo is to cotton what cashmere is to wool. It is also warm thanks to the hollow microfiber (like wool) and most importantly it is breathable & wickable (draws moisture away from the skin). It is reputed to keep you 4% cooler than cotton in the heat.
Bamboo has other wonderful properties too; it is antibacterial as bacteria does not live well in this fabric. It is anti-static so it sits well next to your skin, not clinging uncomfortably to your head. It offers UV protection by cutting out 98% of harmful UV rays so perfect when worn on your head in sunny climes. Bamboo is ideal for sensitive skin so perfect if your scalp becomes sore, dry & itchy during chemotherapy treatment. It is also anti-fungal. Therefore bamboo is ideal for anyone undergoing any sort of medical treatment.