In contrast to other suppliers, they were a pleasure to deal with. One said that I would have to pay $300 - 400 to get a chunk of foam as they have to buy in bulk. Or use layered sheets, each 12mm thick, not a very attractive solution. Shown above is enough foam for 6 waveguides, ranging from 6" - 12" in size. The cost is quite reasonable.
Earl Geddes has demonstrated that horns and waveguides sound better when filled with foam. Not just any foam - reticulated foam is needed to have the right balance of absorption without too much attenuation. The foam is intended to absorb to a greater degree the reflections within the horn that cause sound quality problems. I have not yet tried it, but by all account it is a worthwhile improvement.
What to ask for
The foam you want from Flex Foam is called "Mericell." It comes in different densities, you should ask for 30 ppi (pores per inch). It is also referred to as a filter foam, but it's technical generic name is reticulated foam.
Does it really work?
When I have had a chance to test it out properly, I will be reporting my results, both measured and subjective. I have another shoot out planned where we will compare different waveguides and drivers. The challenge at this point is to find a good way to cut the foam.