Ok, I have used the search option and have not found anything specifically addressing this issue, I know most backyard type AP systems are using media beds, but I thought I would add in what I have found out about raft material and certainly invite anyone with any additional information to feel free to add it to this discussion,.

From my research I have found it is generally agreed on that the Owens Corning "Pink" insulation board contains harmful chemicals and should not be used as raft material. I also found that there was a short time they changed their process and it was ok, but now for whatever reason (financial I suspect, as their product is cheaper than the Dow "Blue Board") they have changed back to their original process and it is still not recommended.

Dow "Blue Board" is one of the raft materials recommended by many, as being suitable for raft use, as the chemical makeup and manufacturing process have proven through use, to not be harmful to the fish. This sounds simple until you visit the Dow website and see they have well over 20 (or more) variances of their "Blue" insulation board. The question now is "Which one do I get???" Well, I have found there are basically two types, by trade name that are suitable, in my opinion. #1 the best and most expensive is Dow "Square Edge". Square Edge is the trade name and it only comes with square edges and is rated at 25psi. This board is thought to be more durable, because of the high psi rating from everyone I have talked to. The #2 choice is Dow "Utility Fit", it is rated at 15 psi. Be careful here as the Utility Fit comes in square edge, stepped edge, and also lap edge. You will want to specify the square edge configuration. But that is not all!! There is more options!! It also comes in what is called "Score board". The insulation is scored length wise on 16" centers for ease of breaking in the construction use, which means it would easily break while you were using it also, which would not be good. So you do not want score board. These are the only two Dow products I know of with the right makeup and configuration for raft material, as recommended by others actually using it, some for over 5 years, with no harmful effects, and good durablility.

Plain closed cell 'White' insulation (the stuff that looks like it is made up from million of little balls pressed together) This stuff is really cheap to buy and can be used, however every time you handle it the little balls rub of so it is kinda messy and probably would not have a long life?? But it is cheap. It also may be difficult to find in 2" thickness at your local supplier, most home improvement stores generally carry it in 1".

Most any of the insulation material listed above is not UV resistant, so you may consider painting the tops of the rafts with a FISH safe, UV resistant paint to protect it from the sun? I will also mention as this has been argued many times over. If you call Dow or any of these companies, (read carefully here) "They will not recommend their product for this use, rafts for AP that is) Please understand it is made for the construction industry as insulation, all of their testing has been for this use. The company would be held financially liable if they recommended their product for ANY other use than this. AP is not their target market for this product, they have not tested for this market and they will not recommend it for this, but that is not to say it is not safe and suitable. Years of use in AP use has proven it to be a good product to use.

At present July, 2013 ballpark pricing for these materials are as follows

- Owens Pink insulation 4'x8'x2" sheets about $28 to $32 per sheet
- Dow "Square Edge" 4'x8'x2" sheets about $38 to $42 per sheet
- Dow "Utility Fit" 4'x8'x2" sheets about $34 to $36 per sheet
- White Styrofoam I do not have an estimate on this but it is cheap probably less than $20 per sheet

Just as a side note, as I do not have much info on it. There is a company that makes pre-formed (already has the holes for net pots and everything) rafts, but my understanding is they are relatively expensive to ship because of the bulk?? You are also limited on plant spacing as they are pre-drilled (the plain insulation board allows you to make spacing whatever you want)

I have also found it is generally recommended the 2" board is the choice for good, floatation, durablity, etc. this seems to be the preferred thickness, by most.

Hope this is of help to some one it is information I would have like to have had a month ago. I have both Dow "square edge" and Dow "utility fit" ordered and as soon as I get a chance to do some testing next month, I will let you know what I think of the comparison of the two.

Please note: I do not sell or personally endorse any of these products or companies, just sharing what information I have.
Thanks for listening