The new Unobtainium electric jacket liner ($197) is designed to zip into the Aerostich Darien jacket (shown below left), but it can be worn under any jacket. Like the vest, it features a shell of reversible fleece and nylon but incorporates heating elements into the full-length sleeves. However, the liner's looser fit doesn't offer as much warmth as the vest (even though it draws 75 watts, as opposed to the vest's 45, in an attempt to compensate). What you get is an inner jacket temperature increase of 5-15 degrees above outside temperature. When the ambient temperature was merely cool, this was very enjoyable. You don't get the sleepy sensation that comes with wearing a heated vest. You don't really feel anything specific, except that you're not cold.