Early Experiments Initial tests made use of small "Balloon Animal" type inflatables. The balloons were filled with water, and the ends were stapled to a sheet of plywood, which was placed at a 30 degree angle. The Great Stuff minimal expansion spray foam insulation was then applied, and allowed to dry. The balloons were then popped, and the water drained. What was left behind was a perfect cast of the balloon's shape. Several things were learned here from these initial tests: Larger Balloons make Larger Tubes! Colored balloons make it easier to pick out the broken balloon material. It is best to put the foam on a plastic sheet base to facilitate later removal. A base of foam laid down first creates a more convincing lava tube analog. The Caves of Mars Project is funded by a NIAC Phase II Grant from the NASA Institute for Advanced Concepts. Copyright © 2002-04 - Complex Systems Research; Inc.