Answer:
Defends your noggin from the hard pavement
The buyer doesn’t want it, the producer doesn’t need it and the user doesn’t know their using it.
Mouth up it gets filled, mouth down it gets empty.
It is something you make after you've weighed your options.
Maritime marauders
A word of five letters, Upside down is the same, A shark does this, But it’s not to blame. What is the word?