All of the following are materials used for urns except?

The materials typically used to create urns include ceramic, metal, and stone, as they provide durability and can be intricately designed to honor the deceased. Ceramic urns offer a classic and elegant appearance, while metal urns are often associated with strength and longevity. Stone urns, commonly made from materials such as marble or granite, can also be quite decorative and are frequently chosen for their permanence.

Cardboard, while it can be used for temporary urns or eco-friendly options, is not generally recognized as a material commonly associated with traditional urn design. It lacks the durability and permanence that many families seek when selecting an urn for the remains of their loved ones. Therefore, cardboard stands out as the material that does not align with the conventional choices for urn construction, making it the correct answer.