Tereré exists specifically because hot mate becomes unbearable in Misiones' subtropical heat — locals swapped the hot water for ice-cold water or juice, flipping the entire ritual on its head.
Yerba mate leaves steeped with ice-cold water or fruit juice instead of hot water, sipped through the same metal straw and gourd used for hot mate. It's carried in a thermos of cold water and shared on the street or at market stalls throughout the day.