The straw I use is the same one used in cheese caves and cheese shops the world over. It is made in France and I have a local affineur selling it to me - he has boxes of that stuff. I do believe that this is buckwheat but I don't see why other types cannot be used. Frankly, I don't know the difference between hay and straw. Is hay more grass and green? If so that I am using straw, but I have seen many Italian cheeses aging in green grassy hay too.
Here are some photos from cheese shops/market in Paris that I posted a while back here. You can notice these mats in many of the cheese displays:
http://cheeseforum.org/forum/index.php/topic,4019.msg30669.htmlHere are photos I took at Murray's Cheese aging caves under New York City. As you can see, all of the soft ripened, young, semi lactics and some of the Tommes are also aging here on these straw mats:
http://cheeseforum.org/forum/index.php/topic,4590.0.htmlTo use the straw, do not put the fresh wet cheese on it. Make sure it drains first. I only use it beginning at day 3, 4 or 5. The straw does not need to be sanitized - that would defeat the purpose. Aging on straw takes advantage of its great moisture control and its anti-pathogenic properties. Aging on straw or wood shelves is very common and traditional. One of the nicest things is that some of the cheese bacteria and microorganisms take a hold on the wood and live there. It then helps the next batches of cheese age.
I do replace them once they begin molding (Usually its the twine that keeps them tied together that begins to mold with blue mold).
I think this answers all of your questions?
By the way John, thanks for the compliments. I have gotten tremendous help on this forum not too long ago so I just pass what I can onto others. Luckily for me, I have came to know several world class affineurs, fromagiers and cheesemakers; all of whom have been teaching me time honored techniques and theories that are not found on many book or this forum, so if I can put it out there to make your cheese better or save you from looming wasteful and frustrating disasters, why not? (Eh, well - as long as I have time...)