A see-through covering on a porch roof will be some sort of synthetic material. The original see-through plastic was plexiglass, an acrylic material that came into prominence during World War II when it was used for aircraft windows. Plexiglass replaced glass because it was more durable, didn't shatter on impact but was just as clear as window glass. Some World War II airplanes still have clear plexiglass windows. It is formed in sheets or corrugated panels which make it easy to work with when building a porch roof.
Another see-through roof option is polycarbonate, a hollow core material. It is formed of two thin sheets with a hollow, fluted core in between. The open core gives polycarbonate more insulating value, meaning it can better reduce heat from intense sun without reducing visibility. It is made in panels, either flat or corrugated, and can be bent to form curved shapes.
Polyvinyl chloride, PVC or generally just vinyl, is another common see-through roofing option. Vinyl roofing generally is in the form of corrugated panels. PVC can be clear or slightly frosted to allow some visibility while blocking most of the sun's rays. It is a common choice for carports, sheds and similar structures. It also is used to build greenhouses.
Fiberglass is another synthetic roofing material with see-through capability. It typically is used in roofing in corrugated panels and generally has a slightly frosted appearance. All basic synthetic roofing materials are available under a variety of trade names, each with its own special characteristics. Some of the more common are Lexan, Acrylite, Lucite, Polycast and Optix.
All synthetic roofing materials, whether flat or corrugated panels, are usually installed with screws that have plastic washers under the heads to seal the holes against moisture. Corrugated panels, the most common roofing style, are overlapped at seams to provide complete waterproofing. All synthetic see-through roofing is durable against such things as hail, and long-lasting.