I've never found these hydroponic cubes & long runs of mineral wool to be anywhere nearly as cheap as buying mineral wool from an insulation distributor. However, someone did post a thread up here in which they rented a new space where the previous owner left a TON of long (un-used) strips of mineral wool (obviously for hydroponics) which he used in the wall cavities. It would be hard to get specifics for the material, but if you can weigh it and get an estimated density, chances are it would be similar to other similarly dense mineral wools. Lets be honest; I doubt you will find coefficients for a product used to grown pot. If you can't find the exact numbers, this would be the only way I could see approximating it without knowing the GFR.
I highly suggest calling up a local insulation distributor. You don't have your location posted, but if you are in the US you can check this place out. They have locations in over 20 states and have great prices it seems nationwide. If there isn't one close by, perhaps you can still get a quote from them to negotiate with other local distributors in your area.