Brent--both the air layer and the larger pot were filled with 100% compost, the vast majority of which began as chopped up cactus pads from my yard. I've heard varying opinions about rooting in compost. So far it seems to be working reasonably well for me, but others report having excellent success with other methods, and some advise against rooting directly in compost. I don't know if that warning extends to air layers, but mine have done quite well in straight compost; however, I don't think that's so much an endorsement of using compost as it is of the easy success of rooting air layers.
Alan--I would normally expect a clear pot to get extremely hot in direct sun (although I've never done any actual testing with a thermometer), so your experience sounds intriguing. It's probably still safest to block as much direct sunlight and heat as possible from hitting the roots, but I may experiment a little with something expendable, like cuttings from my BT, just to see what actually happens. Here in Arizona, ANY color of pot gets quite hot in direct sun, but I've found that sleeving pots inside a bucket or anything else that creates an air space between the pot and the light barrier is plenty--as long as the roots have constant access to water. Also, the bigger the pot (i.e., the greater the soil volume to surface area), the less the soil seems to heat up.