What is the dress code for this tour?

Due to the religious nature of the Cathedral, all individuals regardless of gender must cover their shoulders and knees. You can bring extra coverings (scarves, etc) to put on just before entering the Cathedral. It is also prohibited to enter the Cathedral and climb to the Terraces and Cupola wearing flip-flops, slippers, clogs and shoes with heels.
What can I bring inside the Florence Cathedral?

Visitors to the Cathedral must use mandatory luggage storage (Piazza Duomo n. 38/r) to leave the following items before entry: suitcases, backpacks, and large or medium-sized bags.