Richard bray

Pros/Cons XPS (Extruded Polystyrene) EPS (Expanded Polystyrene) Corrugated Plastic (Twinwall)
Water Resistance High Moderate High |
UV Resistance Low Low High
Durability Moderate Low High J
Buoyancy High High Low
Estimated Cost per sq' $1.10 $.75 $1.60
XPS
Extruded polystyrene is the most widely-used material for aquaponic rafts. It is more durable than EPS, and cheaper than corrugated plastic. Foam should be 2" thick to support mature plants. Extruded polystyrene is usually found in the insulation section of hardware stores, and can be blue, pink, or green. Do not use foam with plastic or foil liners.
The only problem with XPS is that it has a very low UV resistance, which means it will fall apart in an outdoor system. Growers solve this by painting the top of the XPS board with non-toxic paint. This also
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helps prolong the life of the foam; you can expect 2-3 growing seasons out of painted XPS board.
Paint that is safe for aquaponic systems must meet the following requirements:

• Must be labeled "For use in potable containers” or "Food safe”
• Must be designed for use on plastic
• Must not be mildew-resistant or mold-resistant
• Must be fully cured before coming in contact with the water

The most common paint used inside aquariums is Krylon Fusion spray paint. Apply at least two coats to the top of your foam board, and allow it to cure completely. Rinse the boards thoroughly before introducing them to your system.
EPS
Expanded polystyrene is used for rafts that will support small plants. EPS is the white, crumbly foam that is used for packaging, and it falls apart quickly in an aquaponic system. However, it is a much cheaper option than XPS, which makes it a popular choice for many growers.
Three ways to improve the durability of EPS are:

• Use 2”-thick foam
• Cut the foam into smaller, 2’x2’ sections
• Paint the top of each foam section

Expanded polystyrene can last 1-2 growing seasons if it is handled gently and used with small plants, like leafy greens and herbs. Once
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EPS starts crumbling, remove it from the system. Those little white crumbles will clog pipes and filters.
Expanded polystyrene sheets are white, and are usually found in the insulation section of a hardware store. Do not use sheets with a plastic or foil liner.