The short answer is you should use the rough side of your green screen, because it will absorb more light and won’t provide anywhere near as much glare as the smoother, more refractive side of the green screen.
That’s not the end of the battle however, the most important part of improving your chroma key is your lighting.
A chroma key is a special effect that keys out the green background with a different one. If your green screen isn’t lit well, it can end up uneven or have harsh shadows, making the chroma key effect less convincing. To fix this, you need some great lighting equipment!
One awesome option is the Torjim Softbox Kit. It includes multiple lights, with adjustable brightness and temperature. Most importantly, the lights come with softboxes which will diffuse the light coming out — leading to significantly less harsh shadows which can save your green screen shot.
If you want to learn more about setting up your green screen, or are still having issues with your keying: check out this green screen guide for streamers!