Floating beds are grow beds with flotation with holes drilled in it. The holes contain baskets 
with a grow media and a plant. This allows the roots of the plant to be immersed in the water all the time. Floating beds are best for cruciferous plants such as spinach, lettuce, kale, chard, mustard, collards, basil, mint and most herbs. Raft systems can be the cheapest systems to build but take up a lot of space. Here is a PDF report from University of New Hampshire regarding establishing a Raft Aquaponics System and utilizing Hybrid Striped Bass for Plant Nutrient Uptake.
Building an Aquaponic Raft System
There are a few materials needed for an Aquaponics/Hydroponics Raft System. First, 
either a raised or submerged grow bed needs to be created. There are several different ways to do this. Either a preformed bed can be purchased or one can be constructed out of wood, plastic and/or concrete. Also, IBC Totes are commonly used for both the grow bed and the fish tank. Please see the link to the video below which provides information and ideas for setting up your own system.
Sources for Building Materials
There are many sources for flotation material for use in floating raft systems however the general consensus seems to indicate that styrofoam or polystyrene provides the most stable and financially viable flotation material. Small plastic baskets or small plastic pots work well in the flotation and can be filled with lava stone or clay growing pellets in which the seeds can be planted.
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Perlite Growing Media |
Net Pots 3 inch - 10 pack
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Filter Media
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Grow It Clay Pebble growing Media
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Raft - Aquaponics Flotation |
Bell Siphon (Set of 2) |
Read more: Aquaponics/Hydropoponics Grow Media