Canoe Hire Thames How Does A "foam Roof Pad" For Carrying A Canoe Work?

How does a "foam roof pad" for carrying a canoe work? - canoe hire thames

I want a boat when I go camping next week for rent and the site says they offer:
"Dwellingup Adventures offers thick foam pads that provide most of the cars transporting
a canoe. Boats for risk entirly the vehicle owner. "
I have not answered on this, but my question to me (the postage is the really quite expensive), so I wondered if someone has a similar type found "foam padding for transporting boats and how they function and can be used in a normal sedan?