Polyester fabric is a great insect barrier.

This material is sold as floating row cover, and insect barrier. This polyester fabric weighs ~0.6 ounce per square yard, and allows 75% light transmission. A layer of this material is reported to protect plants down to 30o F. Air and water are not affected by this material.

To prevent insect damage cover the row before the seedlings emerge leaving enough slack to allow for plant growth. Cover the edges of the fabric with soil to keep insects from crawling under the fabric. This will prevent problems with leaf miners, cabbage worms, etc. When harvesting, roll the fabric back, harvest what is needed, and then recover the plants being sure to secure the edges with soil.
A heavier weight fabric (~1.5 ounces/yard) is sold as a frost barrier. This is reported to protect plants down to 24 to 26o F. This product should not be used as a floating row cover due to the reduced light transmission. Place this product over your frost sensitive plants when frost is expected. Be sure to remove the fabric when temperatures again reach 32o F. degrees or greater.

To find out where you can find this material in Mesa, Delta and Montrose counties go to http://www.coopext.colostate.edu/TRA/PLANTS/INSECT%20BARRIER%20list%20of%20suppliers.pdf.