A while ago I answered a question in our forum on this exact topic.  And since I get this question fairly often, I'll go ahead and post the content of this response for everyone to see.

Solexx and polycarbonate are both excellent materials for glazing a greenhouse structure, patio, sunroom, conservatory, or anything else. Both materials are a rigid, impact resistant, shatter proof, twin wall material (meaning there are vertical “ribs” running through the panels that create air chambers or flutes between the inner and outer layers of plastic).  Both are treated with an anti-UV coating to help protect against the harsh effects of the sun. Polycarbonate can also come in single layer corrugated style. However, there are some important differences to keep in mind when comparing the two.

Solexx is a rigid polyethylene blend of plastic and comes only in a translucent white-ish color. This is because it’s made to diffuse light so shadowing isn’t as strong underneath the material. As a result of this diffusion, Solexx has about a 75% light transmission rate (meaning 75% of light passes through, or it provides 25% shade). Also, it comes only in 3.5mm and 5mm thicknesses (for reference, 5mm is roughly 1/4 inch). Solexx comes either in rolls which you would purchase by the lineal foot, or in pre-cut panels of about 8 and 12 feet long. Several rolls can be purchased instead of one big roll if necessary. The rolls and the panels can both be 49.5″ wide, and additionally the panels can be 41.5″ wide. The material is easily cut with a fine toothed plywood blade on a circular saw, and may even be cut with snips, scissors, or blades.  It has an 8 year warranty against discoloration and degradation as long as installed properly.  Realistically you can expect 20+years of life from the material.

One distinct advantage Solexx has over polycarbonate is the fact that it can be rolled up and shipped standard ground service. The chemistry of the plastic makes it more flexible than polycarbonate, thus it is possible to roll the material. This reduces the shipping charges incurred, especially when purchasing a small amount of material.

Polycarbonate is much more versatile in regards to the range of options available, and is known by several brand names including Lexan, Verolite, and Dynaglas. Polycarbonate comes in single wall corrugated panels, twin wall panels in 6, 8, 10mm thicknesses, and triple wall panels of 8 and 16mm thicknesses. In addition, it is available in clear, gray, and opal (white) coloration. Each of these combinations will yield a different light transmission percentage, from 35-92%. Polycarbonate is a very common greenhouse covering, typically in 8mm thicknesses (82% light transmission) or 6mm for smaller hobby houses. It is sold in panels either 4′ or 6′ wide and basically any length you need, and polycarbonate is also easily cut with a fine toothed plywood blade. Polycarbonate is slightly less flexible than Solexx, and as such must be custom crated and shipped on a common carrier truck. This increases shipping costs by a fair margin, especially when ordering a small amount.  Polycarbonate has a 10year warranty against discoloration and degradation as long as installed properly and realistically you can also expect 20+years of life from the material.

Both materials would also typically require some kind of installation hardware. Plastic H and/or U channels for Solexx and an aluminum glazing system for polycarbonate, not to mention screws and other small hardware.

Polycarbonate seems to be the covering of choice for many commercial, research, and educational greenhouses.  Solexx can be used in these applications, but seems more in use in a hobby or recreational greenhouse setting.  In fact, we now have Solexx hobby greenhouses in addition to our other hobby greenhouses. Either material is a great choice for glazing y0ur greenhouse.  You just need to weigh the many variables involved before coming to a decision.