Glastonbury (amongst others) is scheduled to be a hot one according to leading forecasters so here are some 'tips' on how to keep cool.
1 - Set up your tent when it gets dark and take it down during the day - but some festivals are too big for this, so perhaps get an extra tent to keep all of your stuff in then use a pop-up tent to sleep in.
2 - Use a ground cover between the dirt and your tent.
3 - Pitch your tent in the shadiest spot in the campsite.
4 - Create a solid sunshade over your tent using two tarps or a reflective space blanket. Tie the tarps or blanket to the shade trees surrounding your tent, leaving a couple of feet between each layer allowing the breeze to flow through.
5 - Pick a larger, cabin-style tent (or a gazebo) with plenty of mesh windows. These types of tents stay cooler.
6 - Place your tent facing the wind and keep all windows open to let air circulate.
7 - Do not put the rain fly over your tent.
8 - Use battery-operated fans. Place a bowl of ice in front of it for even cooler air.
9 - Forgo the tent all together and sleep in a hammock or a mosquito cot tent.
10 - Use a camper-van with air-con (oh wait...)