The best sleds usually have slick, hard bottoms to zip across packed snow or room for more than one rider, which can also speed up the ride. Friction and warmth of bodies help melt the snow beneath them and send sleds schussing downhill much like the runner of ice skates melt the ice beneath them.
The trickiest sleds can be the blow-up variety.
"If inflated properly, it can be as good as hard plastic," said Nate Moore, a sales manager for action sports at REI. "If they're inflated at home, then brought into the cold outdoors, they lose some of the air. It's best to inflate them at the hill.
"The larger the surface, the slower it will go unless it's offset by weight."
That also explains why classic wooden sleds with runners used to be so popular with speed-demon sledders.
"They were wicked fast," he said.
SLED TYPES
Inflatables
These usually come in round snow-tube styles or toboggan length, which can look like a mini air mattress for floating on summer lakes.