'double pains'. if you're asking about putting two layers of glass buried into the cob to create an air gap for better insulation, I would be very worried about moisture build-up on the insides. If cob 'breathes' it gives off moisture, the way double pane windows (from the store) are ruined is if air (instead of argon gas) and/or moisture gets in between them. Of course, I haven't done it, right or wrong. Tys