He happened to see Merwen in orange for a moment, while she was struggling with her sweater. Despite how cold it was, Senku was out in a t-shirt himself, so he wasn't really one to talk.

"Pull here." He told her, gesturing on himself where the zipper was. "It'll be easier if you undo it first."

Other people might ask what she's doing, but honestly it didn't seem that important in the grand scheme of things.