Introduction: Semi-Bivy: Keep Your Sleeping Bag Dry and Warmer

About: I'm a mechanical engineering student and a long-time tinkerer and maker. I've been working with 3D printers since 2012 and have been dabbling in various crafts for most of my life. I have at least some experie…

If you have an tent that has lost or never had sufficient waterproofing on the bottom, then you probably know how unpleasant it is to wake up in the middle of the night and discover that you are sleeping in a puddle. The Semi-Bivy provides an completely waterproof layer that also provides insulation from the ground, keeping you warm and dry.

For the backpacker who wants to shed weight the Semi-Bivy would keep the bottom of your sleeping bag dry when sleeping directly on the ground, even when it's moist. With a tarp to keep the rain off and maybe a bug net you could be conferrable in most conditions (with the right sleeping bag of course) without being trapped in a normal tiny bivy sack.

It could also be added to a hammock setup to keep the wind from blowing all of your warmth away, allowing camping season to extend later in to the colder seasons for less then $15.

Step 1: Materials and Tools


  • Emergency Blanket (The SOL brand is best for this project because it is durable and made to be reused unlike most Space Blankets)
  • About 10 ft of paracord
  • Stretch Cord (Optional, can be used in place of paracord on the last step)(Thanks to mike.southey.94 for the idea to add this.)
  • Electrical Tape
  • Strong Thread


  • Marker (Sharpe works well)
  • Tape Measure or Ruler (optional)
  • Scissors
  • Sewing Machine
  • Lighter or Candle

Step 2: Cutting the Emergency Blanket

The blanket needs to get cut down to fit around your sleeping bag better.

  1. Lay out the blanket inner side up (for the SOL this is the silver side)
  2. Lay out your sleeping bag centered on the blanket. If you plan to have your sleeping pad inside the Semi-Bivy then also lay it down. (If you put the sleeping pad in the Semi-Bivy it would be harder to roll off of it during the night.)
  3. Trace the outline of your sleeping bag.
  4. Add some extra space to the outside, the more space the higher the walls of the Semi-Bivy will be, therefor the deeper the puddle you can sleep in while staying dry. My sleeping bag is 16" shorter then the blanket, so I added 8" extra on all sides.
  5. Cut along the outer line.

Step 3: Making the Channel for the Paracord

For the blanket to form a bowl around your sleeping bag we will use paracord to gather the edges, to do this there needs to a channel the runs around the edge of the blanket.

  1. Cut several sections of electrical tape, about 4-6" long.
  2. Fold over a section of the edge the of the blanket about 1/4''.
  3. Put the parcord next to this fold so that it will be inside of the next fold.
  4. Fold it again, this time for about 1 1/2", to create part of the channel.
  5. Stick it in place with one of the pieces of electrical tape. (near the head and foot there is a bit of a curve, don't be afraid to bunch up the fabric a little)
  6. Repeat until you have gone all the way around, leaving a small opening for the two ends of the paracord to stick out (I put mine near where my head would be but the placement of this is flexible).

Step 4: Reinforcing the Channel

Although the electrical tape holds pretty well, reinforcing it by running it through your sewing machine will help it stand up to the stresses of multiple trips.

  1. Set up your sewing machine.
  2. Start sewing one end of the opening for the paracord. Sew back and forth a few times to prevent unraveling. I used a zigzag stitch on the biggest setting to keep the holes far a part to prevent taring.
  3. Make sure to keep the foot of the sewing machine on the electrical tape to prevent the teeth underneath from taring the blanket.
  4. Sew all the way around until you reach the other side of the opening. Finish off with sewing back and forth again.

Step 5: Tightening the Paracord

Now that we have the channel we can tighten the paracord to give the Semi-Bivy it's shape.

  1. Lay out the Semi-Bivy and put your sleeping bag in the center.
  2. Start pulling the paracord until it is tight enough that the head and foot don' t slip off too easily, but loose enough so that you can easily get in and out and so that it will not constrict your movement.
  3. Cut the parracord.
  4. Either tie a knot and melt it a little with a lighter or candle, or simply melt the ends together. Make sure that you pull the ends of the parracord away from the blanket so it doesn't catch fire!

Step 6: Keeping the Sides Up

Because the sides tend to fall down, letting water in and heat out, we will add some paracord across the top of the sleeping bag.

  1. Get in to your sleeping bag and decide and mark where you would like the strings to be. (I put mine right around where my knees would be and a few inches below my hips so that I could sit up if i needed to).
  2. Cut a small opening into the channel where the string is at each of the marks. (Careful not to cut the paracord)
  3. Add a piece of electric tape to edges to prevent ripping.
  4. Take a piece of paracord or stretch cord and tie it to the paracord that is in the channel.
  5. While in your sleeping bag tie the other end of the piece of paracord to the paracord at the other side, making sure that it is tight enough to keep the sides up but loose enough to allow movement.

Congratulations! Your done! Now it's time to go camping!

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