There is a balance between reducing the number of flats and adding weight/rolling resistance. I have found that 'good' tyres will not suffer as many flats as 'bad' tyres. Tyres with built in kevlar case (not just the bead) are very puncture resistance .. at leas untill they are ~10 year old and have many miles on them (think worn very near the case... ) Adding an old tyre case inside a tyre adds to both weight and rolling resistance.. just so you know. How much weigh is easy. rolling resistance is hard ... person I know tows a rig behind his car with strain metres .. good luck if you want to go that far.