I can get the bottle from room temp to within range in about 20 minutes using only my body heat, but I am 240 and just shy of 6 foot (average size overall). I just put it under my taint and wear boxer briefs. Don't try to put it in the pocket of some basketball shorts under your pants, they will be able to see it. Just get some boxer briefs of tighty whiteys and stick it under your taint. If you're rail thin use the heat pad but I never needed it especially if I microwaved it first. Make sure if you use the heat pad you don't get it too hot.