Insulation basically works with the fact that air is a pretty good (and free) insulator with respect to conduction. It's rubbish with respect to convection and radiation. So most domestic insulators are opaque (and maybe have aluminium foil on the warm side for reflection too), and are basically there to stop the air convecting.
Having your air inside, say, hollow hairs (like a polar bear) is good. Having it inside inches of spun glass or spun plastic is good. It's the degree of fineness in the binding structure that provides the maximum resistance to air circulation by convection.
If you just use the bottles, you are working to a completely different scale. The air can circulate around the outsides of the bottles. To minimise this, you would have to achieve a tight packing, essentially by laying them like courses of bricks, with ends staggered and the sides in physical contact.
The insides, with a diameter of 50 to 100 mm, are probably about the optimal size to set up very efficient internal convection cells. There is a possibility that this insulation would actually be a negative insulator - actually transferring more heat than would occur in free air.
