Air flow through foam

Dear C, I have never done this, but one possibility occurs to me - if you can cut a circular section and place it in a tube, perhaps you could supply one side with some low air pressure (say 40 psi) and use a flowmeter or anemometer on the other side - I don't know that it would give you any absolute measure, but it might be able for use as comparison. Good luck and let me know what you end up doing.

Can you place a foam sample inside a cylinder and use a flow-meter/pressure meter, etc to measure the variances in airflow from the 'downwind' side? Obviously, the cylinder ends would need to be airtight to ensure consistancy. If the foam samples are similar in size and the rate of introduced airflow is constant between samples you should be able to determine density to some degree

What you're talking about here is actually what the boys in the oil bid'ness worry about - flow through a porous medium. The constitutive equation tying pressure drop to flow and material properties is called Darcy's Law and there's a nice discussion of it at http://en.wikipedia.org/wiki/Darcy's_law Experimentally this is a fairly straightforward thing to measure but you're going to need some equipment. You'll have to create a chamber (a tube section) into which you place the foam section to be characterized. (This totally obstructs the flow except for the flow through the pores. Careful with the seals or you'll corrupt the measurements!) You'll need to measure the differential pressure between upstream and downstream. Sensors for this are readily available. Apply a delta P with a fan/blower (push or pull, it doesn't matter), and measure either mass flow or volumetric flow (whichever is of interest to you) with the appropriate sensor (again, these are readily available). It's a fairly simple setup but you do need the sensors. If you can't take the time you might take the samples to a lab (e.g. Wylie Labs) but it's going to cost you.