EDIT: It's floral arrangement foam.
Something just occurred to me -- I used the fishing line to cut up the APS2 result foam to bisect each impact crater!
Neat (and odd) that the difference between .12g and .20g is bigger than the difference between .20g and .28g, even though they are both .08g apart from one another.
You don't see it so much from this angle, but the width
increase of the crater I think is more noticeable as you go .20 -> .28 -> .43 but the increased depth of penetration is harder to see.