Light and tooby for tubby tires.
The Surly Ultra Light Fat Tube's name is cryptic, obfuscating the true use and nature of a very complicated artifact. You may not guess it at first, but the Ultra Light Fat Tube is a butyl tube with a presta valve for use with fat bike tires. And it's light compared to other tubes designed for similar applications.
The Surly Ultra Light Fat Tube fits 26" tires from 3 inches to 4.8 inches.