Which of the following materials is suitable for personal protective equipment (PPE) when dealing with harmful substances?

Plastic is suitable for personal protective equipment (PPE) when dealing with harmful substances due to its impermeability and chemical-resistant properties. This makes it an effective barrier against various hazardous materials, including chemicals, splashes, and some biological agents. Additionally, plastic materials can be designed to provide a complete seal, which helps to prevent exposure to harmful substances that might otherwise penetrate through more porous materials.

In the context of PPE usage, it's crucial to select materials that can effectively protect the wearer from specific risks associated with their work environment. While leather offers durability and some resistance to certain hazards, it is not suitable for chemical exposure because chemicals can penetrate it or degrade it over time. Silk is not commonly used for PPE since it lacks chemical resistance and durability against harsh substances. Cotton provides comfort and breathability but does not offer adequate protection against harmful chemicals and may absorb contaminants, putting the wearer at risk. Therefore, plastic is the superior choice for PPE when it comes to working with harmful substances.