Here are some examples:
* A raincoat is impermeable to water, meaning water can't soak through it.
* Clay soil is often impermeable to water, making it difficult for plants to grow.
* A good seal on a container is impermeable to air, meaning no air can get in or out.
The term can be used in both literal and figurative senses. For example, someone might say a person is "impermeable to criticism", meaning they don't let criticism affect them.