Kong products are ever popular.  They are fun, durable and well designed.

Here's what Kong says about the CrunchAir balls pals:

It’s all about the crunch! KONG Crunch Air creates a crunching sensation that delights dogs while fulfilling their natural chewing and chasing instincts. The KONG Crunch Air features an ideal bounce that is great for interactive play. It’s also durable, making sure that fetch, chase and chew sessions last even longer. Add to that the KONG Tennis material that is uniquely designed to be gentler on teeth and gums and dogs are sure to be rewarded again and again.

Unique crunch sound fulfills natural instincts
Ideal bounce that encourages on-going interactive play
KONG Tennis material designed to be gentler on teeth
Durable for on-going playtime fun
Great for fetching games