Distance Between Walls
There are no clear-cut rules regarding the amount of air space needed between walls to form a part. Smaller and lighter gauge parts seem to require less air space than large and heavy-gauge parts. Sidewalls require slightly more air space typically than bottom or top surfaces. Rule-of-thumb minimums for air space in parts up to 1 ft. sq. would be 3/8" on sidewalls and 3/16" on top or bottom surfaces. Parts larger than 1 ft. sq. should form adequately with 5/8" air space between sidewalls and 5/16" on top and bottom surfaces. It is interesting to note that thin panels can become stronger by increasing the distance between walls.