What process can be used to create large, hollow items?

The process of rotational moulding is specifically designed for creating large, hollow items from materials like plastic. This method involves placing a plastic resin in a mould and then rotating it around two axes while being heated. The heat causes the resin to melt and evenly coat the interior surfaces of the mould, filling it out completely and forming a hollow shape as the mould continues to rotate. The main advantage of this process is its ability to produce complex shapes and large items without joints or seams, ensuring structural integrity and a smooth finish.

The other options do not focus on creating large, hollow items in the same effective manner. Foaming typically involves creating a lighter material through a reaction that expands a polymer but is not suited for large hollow shapes. Transfer moulding is used for making items with specific shapes and components through a different method involving preheated material being forced into a mould, typically suited for smaller and more detailed work rather than large hollow structures. Welding is a method meant for joining materials, particularly metals, and does not apply to the creation of hollow objects. All these differences highlight why rotational moulding is the most suitable choice for creating large, hollow items.