difference 2 compound Arctic Silver and 1-compound

Hi there... what is the difference between 2 compound arctic silver and 1 compound arctic silver. What is better to use? Or does each one serve a different application.
Of course these questions are in relation to flashlight modding of a 5w Luxeon and heatsink.

2 part is epoxy, preferred

1 part is just grease which would get rather messy over time.

I meant Arctic Alumina Premium Ceramic Polysynthetic Thermal Compound (I referred to it as 1 compound) - and the other one is Arctic Alumina Thermal Adhesive.

2 part is used as a thermal epoxy, whereas the 1 part is used for thermal transfer alone where you don't want the two parts stuck together forever.. One might use the 1 part on the outside of a hotlips before positioning it into the mag if they thought it was necessary (not necessary just an example), while they'd use the 2 part to epoxy the luxeon to the heatsink.

Both fill in microscopic pits in the metal to allow for better heat transfer when used in the right amounts.

You shouldn't have a need for the 1 part compound.. stick to arctic silver thermal adhesive or arctic alumina adhesive.