The blue foam in the picture and used as a building material is a closed cell foam and virtually does not soak up water where as the common white foam is an open cell and will. My next project is to make a floating island for turtles made out of blue foam. The outside can be heated with a heat gun to make a rock hard melted surface. I will coat the surface with epoxy and coat it with crushed lava stone for a natural looking rock like texture. That's the plan anyway.
Dow STYROFOAM
Since its introduction in 1948, STYROFOAM Brand insulation, the Blue extruded polystyrene foam, has been a proven performer in millions of installation's worldwide. STYROFOAM brand insulation is made to offer reliable performance over the long term. It's unique closed-cell structure leaves no voids between the cells. The result: high compressive strength and unparalleled resistance to water penetration. Because it stands up to time, you can reuse STYROFOAM brand insulation in may applications, adding exceptional value to your project by saving both future replacement and disposal costs.
Invented by Dow more than 50 years ago and identified worldwide by the distinctive Blue** color, STYROFOAM* products are the most widely recognized brand in insulation today. In the early 1900s, The Dow Chemical Company invented a process for extruding polystyrene to achieve a closed cell foam that resists moisture. Recognizing its superior insulating properties, buoyancy and "unsinkability," it was originally adopted in 1942 by the Coast Guard for use in a six-man life raft. That was the start of many other wartime applications by the Coast Guard and Navy.
STYROFOAM rigid foam insulation also helps protect your home from the damaging effects of moisture. In the early 1900s, The Dow Chemical Company invented a process for extruding polystyrene to achieve a closed cell foam that resists moisture. Recognizing its superior insulating properties, buoyancy and "unsinkability," it was originally adopted in 1942 by the Coast Guard for use in a six-man life raft. That was the start of many other wartime applications by the Coast Guard and Navy. Today, those same properties have found a home in your home – as insulating sheathing that resists moisture and reduces the potential for condensation in your wall where it can reduce the R-value of cavity insulation, contribute to the growth of mold and mildew, and can result in poor indoor air quality.