Here are some excerpts from a supplier: A stone product that is making waves in the landscape construction trade. High Performance Bedding(tm) is an angular, washed limestone material that is both free draining and deters soil migration. As a drainage media, HPB exhibits the benefits of 3/4" clear gravel but is much easier to handle (similar to screenings or granular but without the dirt or small fines that hold water). When placed, it achieves 93 per cent standard Proctor density without the use of compaction equipment. This is of great benefit for under pavers and behind retaining walls. It is self compacting to the 93% range and reduces greatly the amount of settling associated with Granular A/B and sand screeding.