Actually, now I think about it, Ashley always goes off without a jacket on.  he barely feels the cold at all.  I always think he has some in built form of central heating or something and I am always nagging him to put his coat on.  He hates wearing shoes and walks bare foot everywhere---even in winter.  The rest of us would end up with blue feet, I wear thermals and  I noticed that he was especially like that when he was very tightly controlled on his meds.  Maybe it is the extra layer of puppy fat that they put on?