Still wondering what tennis ball to play with? In a recent post, we talked about how to choose a ball based on what's going on inside the ball: What Is The Difference Between Pressurized And Pressureless Tennis Balls? But that's not the end of the tennis ball story. Now, let's talk about the outside of the ball.
If you hadn't noticed, tennis balls come with two types of felt coverings – regular-duty and extra-duty. I myself don't pay a whole lot of attention to this as evidenced by the photo above (taken by me of some balls I had in my bag). I just buy whatever is cheap or handy and, consequently, I have a wide variety of balls around; some regular-duty, some extra-duty.
Does that matter? Well, maybe. “Regular-duty” or “soft court” balls are designed for use on clay courts. As you might guess, tennis balls travel slower on clay courts than they do on hard courts or on grass. The clay absorbs the impact of the ball more readily. Regular-duty balls therefore have a thinner and less fuzzy felt covering so that the balls will pick up less clay when used on those courts.
“Extra-duty” or “hard court” balls are for use on hard and grass courts. Their felt covering is thicker and they have more fuzz on them, allowing them to be used longer on hard courts.
You can easily tell which kind of ball you're playing with in two ways – first, look at the can! But if you're somehow playing with balls that are not in the can (maybe your opponent took them out of the can and you don't want to be rude or weird and ask to look at the can), just look at the brand name printed on the ball. Regular-duty balls will have the brand name printed in red (like red clay) while extra-duty balls will have the brand name printed in black. Useful trivia to know, right?
Why should you care? If you play on clay a lot, and some people actually do, you may prefer the regular-duty balls as they should perform better and last a little longer. And if you play on hard courts or grass a lot, the extra-duty balls would be preferable not only because they will have a longer life, but that extra fuzz may help a tiny bit with increasing the spin you can put on the ball.
Having said all of this, I just played a match last week on hard courts where the opponent provided regular-duty balls. I knew this because I saw that the brand name on the balls was printed in red. However, I didn't bring it up and I certainly didn't complain (I'm sure that would have been an interesting argument). Frankly, at my level, I'm not sure the difference in the two types of balls really matters that much. But when you are buying balls, I recommend you get the appropriate type to get the maximum life out of your tennis balls.