Sometimes your new bought guitar may have string buzz, 9 out of 10 it’s because the action of your guitar is set up too low. You can measure the distance between the strings and fretboard at the 12th fret (depends on your guitar size). If it is too low (less than 1/16’’), the next thing you can do is modifying the height of saddle.
There are several ways you can modify the saddle height. One is replacing the old saddle with a new one. You can buy a new saddle and modify it to the height you want. This is the most direct way. Another way is shim the saddle and adjusts it to the right height. What is the best material of saddle shims? You can try a slice of plastic, plywood or wood.
Some people believe the different shim materials will give the guitar different tonality. There maybe some differences but most of us hardly to tell these differences by our normal ears. There are also debates on using shim vs. not using. Some guitar players (include myself) believe that shims will make sound quality loss no matter what kind of materials they are. To minimize the sound quality loss, you can use shim with the same material as your bridge if you think you must use shim to adjust the action.
Personally I don’t suggest using shim to raise action. Simple and best way is buying a new tusq or bone saddle and replacing the old one. The functionality of saddles is transmitting the string vibration to bridge then to sound board which is the sound generator of acoustic guitar. Saddles made of high density like tusq and bone will do this job well. The shims will increase the probabilities of interfering transmitting of vibration.