I now use Kevlar tires on my Brompton. Before Kevlar I had a flat about every 2 or 3 months. After, not for more than one year.

I asked my local dealer once about slime (the gunk that goes inside tires). He said he would use slime if I needed to ensure I did not get a flat for one trip only e.g. for about two or three weeks, but longterm he said the problem with those products is that they can break up and not only not protect against flats, but maybe cause other problems. He recommended Kevlar.

I pay the extra for Kevlar now all the time wherever it is available. As my old non-Kevlar tires need replacing, each one gets replaced with a Kevlar. It costs more but really pays out in less hassle and less expense recovering from flats. I also always carry at least one spare tube so I never have to mend a flat on the road. Then I mend the tube at home in peace warmth dryness and comfort. When touring far away from home I also carry a spare Kevlar tire as well as 3 spare tubes. Cannot tell you how many times that has helped me especially in hot- hot- Italy.