What Is Rotational Molding?
By Nate Baker
Rotational molding—often called “rotomolding”—is a manufacturing process that creates extremely durable, seamless plastic products. It’s the method used to make high-quality emergency water storage tanks, road barriers, septic containers, and many other heavy-duty items that must withstand stress, impact, and long-term use.
Definition of Rotomolding
Rotational molding is a process in which powdered plastic is placed in a hollow mold. The mold is heated and rotated slowly on multiple axes, causing the plastic to melt, coat the interior surfaces, and form a uniform, high-strength product with no seams or weak points.
Benefits of Rotationally Molded Products
Strength and Uniform Wall Thickness
Because the melted plastic flows throughout the mold during rotation, the walls of the tank form at an even thickness. There are no thin spots, no weak corners, and no seams that could split under pressure.
Durability Compared to Blow-Molded Plastics
Many low-cost tanks are blow-molded, a faster process that creates weaker corners and inconsistent wall strength. Rotational molding, by contrast, produces rugged items that can withstand drops, impacts, temperature swings, and years of outdoor sun exposure.
This process is why rotationally molded tanks are used for:
- Emergency water storage
- Chemical storage
- Septic and wastewater applications
- Crash barriers and industrial containers
Here, we make all of our plastic water storage tanks through rotomolding:
- 30-gallon stackable home water tank
- 55-gallon stackable home water tank
- 300-gallon doorway home water tank
How the Rotational Molding Process Works
The Four Main Stages
- Loading the Mold: Powdered polyethylene (usually food-grade) is placed inside a metal mold.
- Heating: The mold is placed in an oven and rotated in two directions. As the mold heats, the plastic melts and evenly coats every corner and surface.
- Cooling: Once the plastic forms a consistent shell, the mold is cooled with air or water spray while still rotating. This helps lock in uniform wall thickness.
- Demolding: The final product is removed—seamless, sturdy, and ready for use.
Materials Used in Rotational Molding
Most rotationally molded products use high-density polyethylene (HDPE) or linear low-density polyethylene (LLDPE) because they are strong, UV-resistant, and ideal for applications like emergency water storage tanks.
Why Rotational Molding Is Ideal for Water Storage Tanks
Food-Grade, BPA-Free Construction
Rotational molding allows manufacturers to use food-grade, BPA-free plastics—critical for long-term drinking water storage. These materials won’t leach chemicals, even in high heat.
Seamless, Leak-Resistant Design
Because rotomolded tanks have no seams or joints, they are naturally more leak-resistant and stronger than tanks made with assembled parts or blow-molded shells.
At Emergency Water Tanks, all portable tanks—from 30 gallons to our space-saving 300-gallon doorway tank—are built using heavy-duty rotational molding for maximum reliability when it matters most.
Common Applications Beyond Water Tanks
Industrial Containers
Rotational molding is used for industrial bins, chemical tanks, waste containers, and large material-handling products.
Agricultural and Residential Products
Farm equipment, storage totes, kayaks, playground equipment, and even traffic barriers are made with this process due to its toughness.
How to Identify a High-Quality Rotomolded Tank
- No seams anywhere on the tank body
- Thick, even walls without thin or flexible areas
- Heavy, durable feel compared to cheaper blow-molded alternatives
- Food-grade materials rated for potable water
- UV-resistant plastic for long outdoor life
When you invest in an emergency water storage tank, choosing a rotationally molded option ensures strength, safety, and reliability for years—no matter the conditions.
Emergency Water Tanks are made in partnership with Hive Plastics, and when you see a reputable manufacturer like that, you know it's quality work.