I have a 45 pound Malinois/German Shepherd/other mix who loves balls. She is able to deflate them all (and she does this within seconds). I ordered this Jolly Undeflatable soccer ball in size Large over four month ago. I could have gone with a size medium, but the large works for my dog, too. This ball quickly rose to the top as an all-time favorite over here. No matter how many times my dog has sunk her teeth into this one, she cannot permanently deflate it. When she bites into it, it deflates just enough to allow her to get a firm grip on the ball. When she decides to let go, the ball re-inflates itself, going back to being a normal-looking orange soccer ball. I have spent hours upon hours throwing this ball for my dog, and she has bitten into it for what seems like a million times. Every time, it re-inflates back into shape in a matter of seconds. Upon close inspection, it also has too many teeth marks to count on it. Highly recommend this ball if you have a ball-crazy dog. It is one of our favorites!