Downproof just means that the nylon fabric has been hot-rolled. It flattens the fibers and tightens the weave so down won't leak out...
The fabric is great for hammocks, underquilts, etc.
just don't use "coated" fabrics. DWR is ok (durable, water resistant) means it sheds water (mostly). Coated (Polyeurothane or Silicone) is waterproof and good for tarps, bad for hammocks...
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