Snuggie is a popular brand of sleeved blanket. A sleeved blanket is a four-cornered blanket with sleeves, similar to a backwards bathrobe. It can be made of anything blankets are made of.
The answer to this question explains why a blanket does not normally need tzitzis. But the presence of sleeves raises some questions.
- Is the presence of sleeves enough to constitute wearing it in the manner of clothing (derech levisha)?
- Does the arrangement of the four corners not being on all four sides of the body still render it exempt even when sleeves are present?
(In a practical situation, CYLOR of course.)