Twinwall plastic is a generic term given to an extruded polymer

Polymer

A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...

 product. Two layers of polymer

Polymer

A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...

 are connected by flutes to form a sturdy sheet of material which has a wide range of uses. Most twinwall sheets are nominally transparent to allow light transmission, but colored or translucent sheets are also available. The airspace in the cellular space between sheets provides insulating properties, and additional layers of material can be extruded to provide two or three insulating cells, at the cost of light transmission.

Greenhouses

Greenhouse

A greenhouse is a building in which plants are grown. These structures range in size from small sheds to very large buildings...

use twinwall panels in lieu of traditional glazing due to the plastic panels' greater efficiency.