Commercial hearing protection is rated for different decibels of noise. Get the highest level of protection you can afford. You only have one pair of ears and as someone who has lost a considerable amount of hearing from jets and gunfire in the military, I'm here to tell you once lost, it won't come back.
To protect what hearing I have left, I use the electronic type muffs. They can be set to enhance normal voice and background noise, but instantly block loud noises, such as gunfire. I don't know how they work, but they do work well. On those rare occasions where I find myself shooting at an indoor range, I use foam plugs in addition to the muffs.
Spend a few bux and get the good stuff. Your precious hearing is not a place to go cheap.
As the man just said- look for the NRR (Noise Reduction Ratio) numbers on the package- higher number, more noise it stops. The throwaway foam plugs generally are the most effective- NRR as high as 34. I use S&W or Norton muffs- and for REALLY loud stuff, wear plugs under the muffs. Trying to keep what hearing I still have- too many years of thinking that only a wuss wore earplugs.
I prefer the electronic ear muffs, especially at an indoor range. They come in handy when the range officer says something to you while someone next to you is racking off 12 gauge rounds. I paid about $100 for mine and the money is well spent.
I bought a set of Clark earmuffs back in 1986 that set me back over $40, which was a lot back then. Clark makes headsets for pilots, so I figured they would be good - and they were - until I bought a set of Howard Leicht 29dB Thunder earmufs from CDNN Sports (www.cdnnsports.com) for $9.99. They are just as good as the Clarks, more comfortable, and they fold up! I've lost much of my hearing also due to gunfire, so I am trying to preserve what little is left....what?
I use a pair of Western Safety brand muffs that offer a 18db reduction. They cost a whole $1.99 on sale at Harbor Freight. I liked them so much, I went back and bought 2 more pair. 18db is enough to quiet my Mosin to a more than tolerable level.