🔧 Basic Structure of our Thermo Bottle:

1. 
   Double-Walled Construction:
   
   The bottle has two walls, usually made of stainless steel or glass — an inner wall and an outer wall.
   
2. 
   Vacuum Insulation:
   
   The space between these two walls is a vacuum (or near-vacuum), meaning it has very few air molecules.
   
3. 
   Reflective Coating (Optional):
   
   Some flasks have a reflective coating (like silver) on the inner surfaces to reduce radiant heat transfer.
   
4. 
   Tight-Sealing Cap:
   
   A well-insulated, tight-sealing lid prevents heat loss through air movement (convection) at the opening.
   

🔥 Keeping Hot Things Hot / ❄️ Cold Things Cold:

• 
  If you pour in hot coffee, the heat can’t escape easily, so it stays hot.
  
• 
  If you pour in cold water, outside heat can’t get in easily, so it stays cold.
  

A good thermos doesn’t care whether the contents are hot or cold — it simply tries to isolate them from the outside world.

🧠 In Summary:

A thermo bottle keeps things hot or cold by using a vacuum layer between two walls to prevent heat transfer via conduction and convection, and sometimes reflective surfaces to reduce heat loss by radiation.