Which of the following materials is commonly used for slings?

Steel cable is commonly used for slings due to its exceptional strength and durability. It has a high tensile strength, which allows it to handle heavy loads safely, making it suitable for various lifting applications in rigging. Steel cable slings are also resistant to cutting and abrasion, which is essential in environments where slings may be subjected to rough handling or harsh conditions.

In contrast, the other materials listed are not typically suitable for slings. Plastic rope, while lightweight, lacks the necessary strength to safely lift heavy loads. Rubber bands are not designed for lifting and can easily break under tension, making them unsafe for rigging applications. Velcro strips are also not appropriate, as they do not provide the necessary strength and stability required in lifting scenarios. Therefore, steel cable is the standard choice for reliable and safe sling applications.