EPDM:

Ethylene Propylene Diene Monomer (or Terpolymer which is simply a product consisting of three distinct monomers).

EPDM roofs are single-ply membranes meaning there is only one ply of roofing material, not multiple plies laminated together. 

EPDM has been in use on roofs the 1960's and is one of the most common types of low-slope roofing materials. This is because it is fairly clean to work with when compared to conventional built-up roofs. There aren't the odors and fumes that accompany built-up roofs which appeals to many property owners and managers.

TPO membranes are single-ply roof membranes constructed from ethylene propylene rubber. They are designed to combine the durability of rubber with the proven performance of hot-air weldable seams. They have been tested as having excellent resistance to ozone, are algae-resistant, environmentally friendly and safe to install. TPO is highly resistant to tears, impacts, and punctures with good flexibility to allow for building movement.

TPO membranes are installed fully-adhered, mechanically-attached or ballasted. Fully-adhered means that the roof is "glued" to the substrate using a special adhesive. What actually happens is the glue creates a chemical bond with the membrane. Ballasted simply means the membrane is loose laid over the top of the roof, sealed at all penetrations and around the perimeter.

PVC (Polyvinyl chloride)

PVC is classified as a thermoplastic. It is produced by extrusion, calendering or spread coating. Seaming is accomplished with either a solvent bond or a hot air weld. PVC roofing has been used in roofing applications since the 1960's