What is the intended nuance of じゃないか? Is it asking for an opinion after the addressee has put on the item of clothing, expecting the answer to be "yes"?
Thanks Toritoribe, in (1), given that the addressee is not yet wearing the item of clothing, do you get the sense that the speaker is (semi-rhetorically) expecting the addressee to make a judgement just by looking at it?
I've read that section (well, the whole book) in both English and Japanese so it's hard for me to say what's in the sentence and what's in the context, but yes, I got that feeling from the passage. I got a sense from the description of the sweaters, as well, that they did in fact look very warm, although I don't recall the precise wording in either language, but the description was such that it would seem hard to deny that they were warm sweaters.