Floating rafts (also known as deep water culture, or DWC) are the go-to growing method for most commercial-scale aquaponic operations. A raft simply sits on top of your grow bed water with plant roots dangling below into the nutrient-rich water while the raft itself keeps everything supported above the surface.

Choosing raft material for a DWC system

You have several material choices when building your own floating rafts, and each comes with its own trade-offs in cost, durability, and safety.

Polystyrene sheets

Large polystyrene sheets are inexpensive and work remarkably well once cut down to match your tank dimensions. Because the material is soft enough to drill or punch through, you can size the plant holes to fit whatever you’re growing, and enlarge them later if needed.

A big advantage of this setup is that a single, sufficiently large tank can host plants at several different growth stages simultaneously. As seedlings are planted at one end, the rafts slowly drift along the water’s surface, opening up space behind them for the next round of seedlings. By the time a raft reaches the far end of the tank, the plants on it are typically full grown and ready to harvest. You then pull the mature plants, slot in new seedlings, and the cycle continues indefinitely — which is exactly why this approach is so common in commercial aquaponics.

Safety note: only use polystyrene that is food-grade and free of flame-retardant treatments. Those additives can leach into your system’s water and harm both your fish and, eventually, you. If you plan to paint the top surface, skip any paint formulated with mildewcide for the same reason. Look specifically for “Dow blue board,” widely considered the best polystyrene option available. Food-safe white styrofoam (the kind used for takeout containers or coffee cups) is another option, but it’s noticeably weaker than Dow blue board, so keep rafts made from it small to avoid breakage.

Flame-retardant-treated foam

Some Dow blue styrofoam is manufactured with polymeric flame-retardant technology. It doesn’t float quite as well as untreated polystyrene and tends to break down faster, often lasting only a single growing season before it needs replacing.

Plastic

Rigid plastic sheeting or lengths of guttering pipe can also serve as raft material — drill holes through it to let roots hang into the water. Plastic holds up well over time, but it can be less stable on the water and tends to cost more than the alternatives.

Homemade rafts

To keep expenses down, some growers combine plywood with plastic sheeting or scrap foam they already have on hand. Anything buoyant enough to stay afloat can technically work as a raft. The catch is durability: materials prone to rotting in water may need to be replaced every year, which adds ongoing cost and hassle. This route tends to suit short-term experiments better than a permanent setup.

If you go the plywood route, be aware that most plywood adhesives contain formaldehyde, which can stunt plant growth and, at high enough exposure, harm or kill your plants and fish.

Organic styrofoam

If environmental impact is a concern, certified organic styrofoam boards perform similarly to standard polystyrene while being produced in a more eco-friendly way. These boards can also be painted, though that raises the separate question of paint safety and raft color. Some growers believe white rafts encourage more algae growth, while others argue white simply makes existing algae easier to spot rather than causing more of it.

Picking the right material for your setup

Ultimately, the best material depends on the type of system you’re running, your budget, and your experience level. For most beginners, polystyrene sheets offer the best combination of low cost and ease of use. If sustainability matters more to you, organic styrofoam is a solid alternative, and if you’re just testing the waters (so to speak), almost any floating material will do for a trial run.

Whatever you choose, think carefully about whether the material could introduce harmful substances into your system, and apply the same scrutiny to any paint or coating you add to a raft.

Finally, make sure your rafts can float freely within the trough rather than fitting snugly against the sides. A tight fit might reduce algae growth, but it also prevents the raft from drifting naturally as plants mature, which breaks the continuous planting-and-harvesting cycle — you’d have to shift the rafts manually instead.

When in doubt, start with basic polystyrene sheets to get your system running, and you can always switch to a different raft material later as your setup evolves.