Polycarbonate and acrylic are both stronger than glass. Acrylic has 10 times the impact resistance of glass, but polycarbonate has 250 times the impact resistance of glass. Acrylic has a high gloss finish and is more transparent than polycarbonate. The difference is negligible at first, but the gap will widen as polycarbonate will yellow, as a result of sun-exposure. Over time both will lose visual clarity, the difference being that acrylic can be polished to regain it and polycarbonate cannot be. For the purpose of growing in a greenhouse, polycarbonate may be the better choice because it is much more resilient. But for aesthetics, such as a home-attached structure, acrylic may be a better choice if you want a something stronger than glass.
Looking for installation accessories?