I have made felted balls before and I have seen many different varieties. These Woolzies are substantial. Large in size, and work great. I have tried using a ball made of aluminum foil and it works the same way in the dryer, but boy is it loud. 

Woolzies are 100% pure new zealand wool dryer balls that do everything that conventional fabric softeners do plus they reduce drying time by 25%. They are money back guaranteed to last for at least 1,000 loads!
Woolzies have no chemicals at all and are also hypoallergenic so are safe even for people with wool sensitivities. 

I received one or more of the products mentioned above for free using Tomoson.com. Regardless, I only recommend products or services I use personally and believe will be good for my readers.