An insulation sleeve including a protrusion formed on a sidewall of the cup which is caught by a finger of a user's hand is provided, in which, in a case where the cup is filled with a hot content, the user can easily and safely grip the cup, without slippage, at movement with the cup. The insulation sleeve includes a sleeve body having a hollow portion which is formed when a force is applied both corners of the folded sleeve body so as to accommodate and support the cup therein; and a pair of protrusions formed by a -shaped, ⊥-shaped, ⊂-shaped or L-shaped cut line provided on the sleeve body, and protruding from the sleeve body in an outward direction when the hollow portion is provided, so that the protrusions are caught by a an upper portion of a finger of a hand gripping the sleeve body.