Development of the Lightweight Poncho began in 1966 after the U.S. Army Vietnam Tropical Combat Uniform Board stated that not only was the standard poncho too heavy but that its shiny finish when wet constituted an operational hazard.1 Though it was identical in design to the standard poncho, the new lightweight model was only half the weight thanks to its 1.6-ounce nylon rip-stop fabric construction.
Only the outside was coated in polyurethane, but both sides were water repellent treated. This prevented "wicking" on the uncoated inside and on the outside caused the rain to form in drops that broke up the shiny appearance of the poncho when wet.2
The new lightweight poncho was subject to monsoon testing in Vietnam between October 1966 and January 1967 and though some users reported that insect repellent dissolved the polyurethane coating, it was concluded that it should be procured for issue.3 Initially it was only produced in OG-207, but later in the war an ERDL camouflage version became available. Natick Labs also manufactured an experimental tiger stripe model towards the end of the war.
1. Summary of Proceedings of United States Army, Vietnam...Tropical Combat Uniform Board. (22 November 1965)
2. Support To United States Army In Vietnam - Clothing & Organic Materials Vol II (United States Army Material Command Aug 1968)
3. Final Report - Tropical Combat Uniform (Ponchos and Groundcloths) - ACL-84.4/67I and 84.3/67I (Army Concept Team In Vietnam June 1967)