Should we be using poly bags or are they bad for the environment?

Issue #1 - Energy required to manufacture plastic vs. paper

It takes more than four times as much energy to manufacture a paper bag as it does to manufacture a plastic bag.
The primary reason for this is that it takes only one-eighth as much material to produce a plastic bag.

Issue #2 - Pollution

The majority of kraft paper is made by heating wood chips under pressure at high temperatures in a chemical solution. The use of these toxic chemicals contributes to both air pollution, such as acid rain and water pollution.
Paper sacks generate 70% more air pollution than plastic bags.
Paper sacks generate 50 times more water pollution than plastic bags.

Issue #3 - The Landfill Crisis

Plastic film is estimated to account for less than 3% by volume of municipal landfills compared to 97% other materials.
By weight, plastics account for only 7% of the U.S. landfills compared to 36% for paper.

Issue #4 - Transportation

It takes seven trucks to deliver the same quantity of paper bags contained in one truck of plastic bags.

Issue #5 - Recycling, Reuse and Source Reduction

It takes 91% less energy to recycle a pound of plastic than it takes to recycle a pound of paper.
Secondary use of plastic bags reduces solid waste by reducing the need for new bags.
Plastic bags are 90% thinner than their paper alternatives and the use of these thinner, superior films has had a significant impact on reducing the volume and weight of plastics in municipal landfills.