"Drop-out" perlite is perlite which didn't have enough moisture in it during processing to expand properly ---and so it didn't expand, or it didn't expand enough. As a result, these heavier, large perlite particles "drop-out" of our furnaces. Regular perlite also has been used by people who want something to soak up more moisture, or provide more drainage in both corrals and stalls.

After many years of hearing about this unusual use of perlite, we finally got some pictures (see side menu bar) of this "unusual and unexpected" use. Apparently, the perlite is simply spread on the ground "as is" providing less compaction and more drainage.