Jon,
I apologize for the lack of detail
I have used 200 denier nylon, the same stuff that is used to make flags. It is very durable and is moisture resistant. I am in process of finding out how 'washable' they would be in extreme cases. There is currently no material on it that would be damaged by moisture. As you saw in the picture, I've incorporated a mesh for under the rods to allow as much breathing as possible to the table and rods. This was designed this way because as you probably know, many people have their foosball tables in their basements. I wanted to avoid a 'heavy' cover that retained or collected dampness. I send each cover in a poly bag that could be used to store it when you have to pack it away.
Thank you for the interest! Let me know if there are any other questions I may answer.
Best,
Ken