+1 on Das Boot! It saves you having to carry a spare folding tire, so it's much lighter and more space/weight-efficient.

I use the boots made by Filzer, sold at Mountain Equipment Co-op in Canada for about $6.50 Cdn (and overpriced at that). They're about comparable with Park. They are made of some too-soft material made to look like a carbon fiber weave. For that sidewall cut illustrated above, the Park or Filzer boot would likely hold long enough to get home. Had the cut been to the tread itself, I doubt if the Park boot would have held; I know the Filzer wouldn't, unless you used two or three layers. I cut the Filzer boots in half, and when I need to boot a tire, I use two pieces, one over the other. This is usually good enough for about 100 km maximum. At that point, the boot wears thru, the tube sticks out, and you get another "wear" puncture, denoted by the hiss-hiss-hiss sound as the tire rolls over the cut.

Another thing I carry is a defunct credit card to use as a boot. This usually keeps the tube from poking thru the hole in the tread, but when you remove the tube after the ride, the card will be completely destroyed, broken into strips. Sometimes you'll get a junk mail from some credit card company with a sample card made of a material slightly thinner than a real credit card. This is ideal; put this card into your seat pack; you can use it to supplement the boot. The tire will make a tiny "bump" until you get home, but that's OK; you are going to chuck this tire anyway.

L.