These bad boys come straight from Scott's Freeride range of clothing. The crash-friendly over-the-knee cut is preshaped with strategic mesh panels for a more mobile fit. It still takes a few rides for the thick fabric to move with your legs rather than them rattling around inside though.
Crash resistance and durability is great and a rubber welt below the waist bridges any back plate/armoured undershort gap. The mesh lining also helps to disperse sweat, although these are still hot pants if you're pedalling hard. The price is reasonable though and they're also available as full length race pants.