Has anyone used that 1/8th inch or a little thicker Black Foam underlayment under a nail down Floor? I have heard both sides on using it and purchased some but I am now getting cold feet on using it under my 5/8 Bamboo Floor? I know the old school is the 15lb felt but like the thought of improved products. What say y'all? Cheers

Foam holds moisture, Asphalt repels it.

I guess I should explain a little more, this will be going above grade on a wood substraight so I believe I will not be needing the moister barrier? I would like to put the best product under the floor. I think I better play it safe with a felt or heavy wax paper. Cheers

In your case, the underlayment is only there to ease installation and sliding boards in the rows, and squeaks from wood to wood, if it is not used. No need for any moisture retarding properties. You could use newspaper.

Does it matter which side of the shingle paper you put down on the subfloor or are both sides the same? thanks

On roofs the side with the lines goes up as a guide so you can overlap it and still keep it straight on runs. I would imagine that it really does not matter which side is up but I personally have always installed it lines up out of habit.