Place a bottle in wet mortar as the basement wall is being constructed. Point the bottom of the bottle to the outside of the wall and the top of the bottle facing inside. Place another bottle of equal size next to it, continuing until you have a complete row.
Pour more concrete into the concrete form so the bottles are covered, then add another layer of bottles on top of the previous one.
Repeat the process of adding rows and pouring concrete until the wall is fully formed. As the wall cures, trapped air in the bottle helps insulate the wall. The bottles don't need to be closed, but you can add caps or corks to them if you prefer.