Here's the thing I'm talking about from the HH website page
The OverCover WEIGHT: 3 oz.
Originally the OverCover was offered as an optional accessory because only a small percentage of campers will be spending time camping in dry, subfreezing temperatures. However,some reports are coming in saying that the OverCover is being used in above freezing temperatures with great satisfaction as it keeps interior temmperatures about 10 degrees warmer inside the hammock enclosure with noticably reduced condensation.
INSTALLING OVERCOVER The OverCover is placed over the hammock netting with the air hole at the head end of the hammock. The OverCover is secured under the perimeter of the UnderCover. To install the OverCover, thread the elastics at each end of the OverCover through the holes at each end of the UnderCover and hang elastics onto the hook of the fly tensioner. Next, thread the hammock side elastics through the side openings on the OverCover. If the UnderCover is already installed, make sure the side elastic is threaded through the Over Cover first and then the UnderCover. Fresh air is available through the air hole near the occupant's face. Changing position in the hammock acts as a bellows and automatically pumps fresh air through the air hole. Condensation which may form on the inside of the breathable OverCover will be absorbed and will wick through the uncoated fabric and evaporate through the dry air moving between the OverCover and the rainfly. The OverCover may also be released on one side and the loose half can be tucked between the netting and the OverCover on the opposite side to expose half of the netting and still block the wind from one side.
"Civilization is the limitless multiplication of unnecessary necessities." - Mark Twain
“I go to nature to be soothed and healed, and to have my senses put in order.” - John Burroughs