Lowe has round tubes so they are hollow, no foam.
And by the way that is not something you want to do, it adds weight and if you ever get a leak the foam with saturate and you are hosed, no way to undo it.
Also popular myth, if you fill the tubes with air the have more buoyancy, not true.
The only way to increase buoyancy is to increase the size of the tubes or lose weight..