One of the differences is in how they are measured: tubes are defined by their outer dimensions (OD) and shape, while pipes are defined by their internal diameter (ID) as this determines the capacity.
Plastic tubes (whether square, rectangular or round) are usually measured by their outside dimensions and wall thickness. They are often used for protective purposes, spacing, framing, flags and many other purposes. Pipes, in contrast, are often used for transporting liquids or gases and are defined by their internal diameter. At MKM Extrusions, we offer both square/rectangular tubing and round tubing as part of our stock product range. These profiles are made from rigid PVC, and some sizes of the round tubing are also available in a flexible version. None of these tubes are designed for transporting fluids or gases. Instead, they are used for general-purpose applications, which can vary depending on the project.