There are numerous reasons for buying a Bivy Sack. They are small and lightweight. They allow for quick setup of camp and allow you to find a smaller campsite.

Hobbyists of hiking, biking, climbing and mountaineering have been moving towards more minimal gear. Lighter and smaller gear makes it easier for them to travel farther, bike longer, and hike higher.

Modern fabrics have created a very diverse set of materials that are used in Bivy sacks. Some bivy sack materials serve different purposes or have different strengths and weaknesses. In this article, we’ll explore some requirements of the fabrics as well as look at some of the most common bivy sack materials used in today’s models.

Bivy Sack Material Overview

In general, the top and the bottom of bivy sacks are made from different materials. The fabric on the bottom of the bivy sack, underneath your sleeping bag, needs to be waterproof and strong. It needs to keep your sleeping bag dry. It also needs to be strong enough to prevent tearing or puncturing from the rough surface of the ground as you move around in your sleeping bag.

The top part of the bivy sack is the part that encloses you, so it needs to be lighter weight, waterproof, breathable, and durable. Body heat and the vapors from your breath can cause condensation on the inside of the bivy sack, that is similar to a one-wall tent. This can cause your sleeping bag to get wet and reduce its insulating ability. However, if the bivy sack is made from breathable fabrics, it can help to reduce the moisture and condensation issue.

Some construction features will also enhance the benefits of the materials. Taped seams increase the waterproofing of bivy sacks. Multiple zippers or a full-length zipper provide ventilation and reduce condensation by allowing you to leave openings in the bivy sack in any areas where you feel too warm. A bivy shelter with a hoop that holds the sack up above your head and mesh netting allows for more ventilation and more room. However, these items will also make the bivy sack weigh more.

Different Materials Used for Bivy Sacks

Silnylon is made from silicone and nylon with a ripstop weave. The silicone adds strength and the waterproof nylon makes it a good fabric for the bottom of a bivy sack. In addition, the ripstop weave prevents any tears from ripping further. Since, it is not breathable, it is not ideal for the top of a bivy sack. Though it is often used in lower end models to help reduce cost.

Gore-Tex is a laminate made from stretched polytetrafluoroethylene (PTFE) or Teflon. It is waterproof, windproof, and breathable. So, it is well suitable to be used on the top of bivy sacks.

Epic is a combination of polyester and silicone. It is breathable, windproof, and water-resistant, which is not the same as waterproof. It is not a coating, so it is washable. Since it is breathable, it is suitable for the top of bivy sacks, but other fabrics that are waterproof might be better choices.

eVent uses a dry technology to get rid of moisture instantly. It is waterproof, breathable, and washable. Since it is used in gear for fire departments, police, and the military, it is also fire resistant and offers protection from hazardous substances. It is a good choice for the top of a bivy sack.

Like Gore-tex, ToddTex is also a laminate made from stretched polytetrafluoroethylene. It provides breathability and waterproofing. However, it has also been treated to be fire-retardant. It is suitable for the top of a bivy sack.

Momentum is windproof but only water-resistant. Since it is only water-resistant and is not mentioned as a breathable fabric that removes condensation, it does not seem like a great option for a bivy sack.

Pertex Quantum is made with two fiber thicknesses. On the inside of the fabric is a thicker fiber that absorbs moisture and wicks it to the thinner fibers on outside. The two fibers contribute to its softness. This makes it waterproof, wind resistant and breathable.

Sympatex is waterproof, windproof, and breathable. It is different from most of the other fabrics because, instead of using pores to allow condensation to escape, it uses a wicking technique. When measured for waterproofing, it receives a very high rating. It is a good fabric for the top of a bivy sack.

Textrem is 100-percent polyester with a polyurethane coating. The coating makes it waterproof and windproof. It would be good choice for the top of a bivy sack.

Powertex is a coating that is applied to the fabric, making it weatherproof. It could be used for the top of a bivy sack.

Conclusion

A bivy sack needs to have material on the bottom that is strong and waterproof. The material on the top needs to be waterproof and breathable.

The best materials for the bottom of a bivy sack is Silnylon.

The best fabric for the top of a bivy sack are Gore-Tex, eVent, Toddtex, Pertex Quantum, Sympatex, and Powertex.

The best bivy sack would have silnylon on the bottom, and eVent on top, but any of the other fabrics will provide a waterproof and breathable cover. Momentum and Epic have been left off of the list because they are only water-resistant.

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