Here's a little video showing the construction of a super-insulated restaurant oven. The "basket" design seems to be a pretty inexpensive and effective way to insulate -- not necessary for every oven, but for ones that really get regular use, I think it's worth it... It's a pretty big oven, too, so I opted for hand-made mud bricks instead of mud over a sand-form. For more details about the technique (including brick-making, as well as photos of how well the insulation protects the bamboo), there's an extensive post and pix about the Gathering Together Farm Oven, which was similarly (re)built. . . .

Insulate! Insulate! Insulate! This oven gets used about 5 days a week, so it never cools down -- partly thanks to 11" of insulation under the hearth (vertical wine bottles in perlite), and about 8" of loose perlite over the dome (poured into a basket made of bamboo covered in clay/plaster soaked burlap and mud). I built it for a local CSA farmstand restaurant (gathering together farm). The whole story (build and repair) follows, complete w/photos of making our own bricks and laying them up from the inside out! The oven started in a public workshop; folks came to make mud and learn and we . . .