physics materials not showing up?

I am creating a 2d platformer to help me get to grips with unity.

I am try to make it so when you run and jump into a wall you fall instead of sticking there by pressing a or d depending on what side the wall is on.

I googled around and found out that putting the ice material on the wall would make the character slide down so i went and imported it by going to assets - import package - physics materials.

But when i went to the box collider on my wall and tried to add a material the box is empty and has a blue horizontal capsule saying None.

I am sure i imported them correctly they are in my assets folder.

What can i do and if i get this to work will my character slide down?

Thanks in advance for help!