Yes, you can say a sweater is cozy. It would mean it's warm and comfortable. It might also suggest that you've had it a long time and you're very fond of it.

Cozy (US) or cosy (UK) tends to collocate with space as opposed to a texture i.e. a cozy apartment or a cozy home. If in reference to a thing like a bed, chair or, in your case, a sweater, it's is more about the feeling that that thing makes you feel. i.e. I am cozy in bed. With that said, it would be common vernacular to shorten such collocations down to 'this is a cozy bed' or 'a cozy sweater'

I absolutely agree with Tim, you can say that a sweater is cozy. The word "cozy" is often used to describe something that is warm and comfortable, which is a perfect description for a sweater. Other adjectives that could work are: Comfy Soft Warm Snug So, a sweater can be described as cozy, comfy, soft, warm, or snug. Each of these words highlights a slightly different aspect of comfort that a sweater might provide.

I think many English speakers would expand the sentence a little and say 'I feel all nice and cosy in my warm fluffy sweater" . Associating cosy/cozy with being inside a space. This sweater is comfortable is fine. But there is no reason why you can't say this sweater is cosy/ cozy.

Hallo