perlite and like material is totally non-nutritional and unnecessary - sand as well, although the worms can use some fine grit, so a bit of garden soil is nice - if you need to 'lighten up' the bedding, use carbon materials like sawdust, and work the bin over once in a while to prevent wet areas

Bill

As long as the worm bin is three feet or less tall, you really don't need special materials and I would never use an inorganic material like perlite in a worm bin. You want a bedding that won't pack easily, but this whole notion about necessary aeration is way overdone.
The fact is that the action of the moving worms through the bin provides all sorts of aeration - as long as we don't disrupt the process too much by digging around in there.