That's rockwool. It's enviro safe in that it's made from rock which won't hurt the environment. However, if the field you're flying on is used for grazing, it's as bad as fiberglass.
Exactly what bill said...
It's really not that difficult... there are two kinds of "recovery wadding" basically-- expendable and reusable.
Dog barf, sheet wadding (Estes type), green leaves, green grass, cabbage or lettuce leaves, etc. are "expendable" wadding... they make one flight, and that's it... IF you manage to find Estes sheet wadding on the ground, it CAN be reused, BUT sometimes it's very hard to find it because it disperses on the wind after ejection as it flutters down. Dog barf and green plant material will of course completely disperse, more or less...
Reusable "wadding" is like nomex heat shields, Teflon pom-poms, ejection pistons, etc. These are intended to be reused after each flight, and thus should obviously be tethered to the rocket so they return with it. Baffles of various designs usually fall into this category as well, though baffles are often used with a single sheet of wadding or a heat shield just as a "final layer of protection" against hot gas or stray bits of BP getting through the baffle...
We can also break it down into two different KINDS of recovery wadding-- biodegradable, and NON-biodegradable. Waddings made from paper products, green plant leaves, and other such things are biodegradable. Things like rock wool, fiberglass insulation, pillow or mattress ticking (stuffing), flameproof artificial fibers, Teflon pom-poms, foam plugs, etc. are NON-biodegradable.
NON-biodegradable materials SHOULD NOT be used as "expendable" waddings, that is, deliberately ejected from the rocket with no intent of recovery or reuse. Rock wool is non-biodegradable, thus shouldn't be used. Fiberglass, pillow ticking, and artificial fiber insulation is the same. One material that is commonly used in competition is foam plugs cut out to slide just inside the body tube, to act as a recovery piston... usually made from lightweight Styrofoam. Competitors like them because they're very lightweight and don't take up much space compared to alternatives, BUT, they also commonly fly them in "expendable" mode and eject them from the rocket to flutter down to who-knows-where on their own... This is irresponsible and would PO any landowner, especially after a contest where dozens of foam plugs would be littering the site here, there, and yon... It's a simple and easy fix to simply use a sewing needle to pull a length of thin sewing thread through the plug with a tail a few inches long, and tie that off to the shock cord or screw eye, and thus recover the foam plug "piston" with the rest of the rocket... that's the responsible thing to do. Of course Teflon pom-poms and nomex heat shields should be attached to the rocket and recovered with it.
Again, it doesn't matter if the material is biodegradable or not if it's REUSABLE wadding attached to the rocket... but if it's EXPENDABLE wadding that will be blown out of the rocket to flutter down on its own, MAKE SURE ITS BIODEGRADABLE, and thus won't pose (much if any) of a litter problem or pose a risk to grazing domesticated animals or grazing wildlife...
Lets respect our landowners and field hosts...
Later! OL JR