Also known as: 二人マフラー, ダブルマフラー, 2人マフラー, 連マフラー, あったかあったか
A Scarf worn by at least two persons. Sharing a scarf usually suggests some degree of affection between the wearers.
On Pixiv, the tag 二人マフラー (couple muffler) is used for a scarf shared by two people and 連マフラー is used for three or more people. あったかあったか is a Scene Reference to a particular scene in K-ON! Episode 7 "Christmas!" where Hirasawa Yui notices her sister Hirasawa Ui is missing her scarf and she decides to share half of her scarf with her.