You can’t melt fat off one spot like butter on toast. Human fat isn’t a puddle waiting to drip out. It’s stored inside living cells. To get it out, your body has to chemically unlock those cells (hormones → enzymes → fatty acids into the bloodstream). A hot wrap on your arm doesn’t turn that switch, and a cold room won’t make your arm donate fat first.

Think of fat cells as tiny storage lockers. Heating the hallway (your skin) doesn’t open the lockers. What opens them is your body’s fuel demand and hormone mix (low insulin, higher adrenaline/noradrenaline), which is a whole-body call.

About the “fat liquefies around 40 °C” idea. that’s a lab fact about pure fat, not how biology works in vivo. You cannot control where you lose the weight from.

Hope this answers your question.