Thanks to its thick layer of springy sub-tread rubber - called SmartGuard - the Marathon Plus is virtually immune to through-the-tread punctures.
As with the Conti Contact Security, even drawing pins won't penetrate. The steelbeaded sidewalls are gumwall and are fairly tough too. Where the Marathon Plus scores over the Conti is its vast range of sizes - including 700x25C. This takes 115psi (8bar) and it rolls surprisingly well, even if the handling is somewhat leaden. It wasn't a lot slower than the competing product by Hutchinson, though it might add 2-3 minutes to a 40-minute commute compared to the fast Michelin Krylion Carbon. There's a Scotchlite strip and dynamo track on the sidewalls. Apart from the slight speed loss, the only real negative is the difficulty in fitting them: I needed a helper and a pair of Pedro's Milk Levers. Still, they're so unlikely to puncture that this isn't a job you'll do often.