Most ex NZ army bivvy bags are made of reflex. They are a great design, lovely and roomy, insect screen etc but the reflex material itself is not renown for being very waterproof. Fine for under a fly/tent etc, but directly out in the elements they wont keep you completely dry.
We had gortex wet weathers for maybe a year or so in the mid 90's, and they were fantastic but it was too expensive for the bean counters, and the rest as they say is history. Davey Hughs' book covers the grief he had trying to make wet weathers on contract with the Army supplied inferior fabric.
Don't know what material the NZDF are using today, I just know that my British Army issue goretex bag still works fine. Goretex really still is the gold standard.
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