Single sided 2 inch tape
This is for use for joining the various polyethylene waterproof membranes. It is 2" wide.
VentureTape 1585CW-P2
http://www.venturetape.com/product.php?productid=1340&cat=50&page=1
It costs about $13.50 for a 222 foot roll.
http://www.theenergyconscious.com/wea2114.html