Waterproof Bag Materials
Just why are DUI waterproof bags superior in construction and performance? We begin with high quality trilaminate material. Here are the reasons why a DUI trilaminate waterproof bag is the choice for operations where mission success is critical.
Trilaminate vs. Bilaminate
There are several different types of materials available in the manufacturing of waterproof bags. The purpose of the bag usually dictates the material and the manufacturing techniques used. This information serves as a comparison between two of the most popular materials – trilaminate and bilaminate. These materials vary in performance and cost.
Trilaminate (3 layer) material owes its light weight and toughness to materials developed for CBR (Chemical, Biological, Radiation) protective clothing and portable structures utilized by NATO forces. Butyl rubber laminated between high tenacity nylon layers makes for:
- Light weight and durable dry shell
- Fast Drying
- Low friction, slick inner surface for ease of entry and removal of interior items
- Flexible, low bulk
- Abrasion Resistant
- Quiet material
The butyl rubber provides the waterproof membrane. Protecting this membrane you have a layer of nylon both on the inside and the outside of the material. This high tenacity nylon has proven to stand up to abrasion over long periods of transportation time and/or high vibration. It also serves to protect the waterproof barrier from punctures and abrasion inside the bag from its cargo.
Seam Construction and Coating: The seam construction used on the waterproof bags is a fold over, double stitch style and is known for its strength and durability. To insure waterproof seams, they are coated with three layers of a hand-applied urethane that completely penetrates all four layers of the fabric seams and thread. This level of coating totally saturates the fabric and makes it impenetrable. The coating is very flexible and will not peel or crack even under extreme cold or heat conditions. If there were to be a seam leak it can be easily repaired at the field level, which consists of reapplying a small amount of the urethane coating.
A bilaminate material is made of two layers. A waterproof polyurethane coating on the inside provides the waterproof barrier and the outer material is usually a pack cloth made of nylon – example 220 Denier or 420 Denier thread. These two materials are laminated together to form the bilaminate. The material itself is durable. However, it is easy to abrade the inner polyurethane film from the inside because there is no protection from sharp or abrasive edges and whatever is inside the bag rubs against that interior and causes wear on the polyurethane film.
Also, the polyurethane coating on the inside of the bag “grips” and is not a slick surface and makes it difficult to remove items from the bag or place them inside the bag. In a time sensitive situation this can be critical.
Because it is a simpler laminating process than the trilaminate, the cost of the fabric is about 1/3 the price of trilaminate, and the manufacturing process is cheaper as well.
Manufacturing technique usually consists of a urethane heat tape applied over seams and that creates the waterproof seam. This process is cheaper because there is less labor involved in applying heat tape via a heat taping machine as opposed to the hand coated urethane seams. However, it is sealed only on the top.
Heat taped seams can be prone to peeling or cracking, especially when exposed to high heat or cold. The outer sides of the seam tape are the weakest points. This is because over time and with normal flexing and pulling and movement, the film can blister or bubble and separate from the base material. Much like a blister on your skin, it is easy to rupture and when punctured will cause the bag to leak.
Bilaminate material has also been known to delaminate which is the separation of the outer nylon from the inner polyurethane coating. When material delaminates, there is bubbling. The symptoms are the same as listed above and lead to punctures in the material.
In addition, corners and curves where seams overlap are weak points because of the application process during manufacturing. Whenever you start or stop the heat taping machine this causes irregular heat when the tape is laid and can cause the bond between the film and fabric to be weakened and thus prone to blistering.
Field repairs are more difficult with a seam leak in this type of bag because the patching material has nothing to soak into creating a mechanical bond. It is best to use a heat tape machine to fix it. In addition, it is sometimes difficult to detect the exact spot of the seam leak when testing because the trapped water can migrate under the tape and pop out in a completely different location than where the actual leak occurs.