The manufacturer informs:

Velda's plant baskets are made of high-quality and very durable plastic.

They are ideal for transporting newly bought plants and for moving plants in preparation for the winter months.
Some more robust species, in fact, can even remain in the pond during the winter as long as you move them to particularly deep spots; other more delicate species, however, such as tropical water lilies, cannot withstand the harsh winter temperatures and need to be moved indoors to an environment more climatically suited to their characteristics.
In such cases, the aid of a plastic cultivation basket is almost indispensable.

The baskets also prevent root dispersion while ensuring proper water circulation.