Glossary of Ultralight Films: Technical Properties, Differences, and Applications
In the ultralight and long-distance hiking community, there is a constant search for lighter and more efficient materials. In recent years, specialized films have come into focus. Highly specialized, cross-linked films offer impressive advantages: they achieve tensile strength comparable to established materials like Silnylon, yet they often weigh only half as much and are far more affordable. However, like all materials, there are pros and cons. This article aims to shed light on the different types of films, their technical properties, and their applications in the ultralight sector.
However, many terms are used in the community, which sometimes refer to the same material but often to completely different ones. This often leads to confusion, especially when it comes to films used for specific purposes such as groundsheets or tarps. To bring some clarity, we will explain the most common names and materials below and show what properties and differences actually lie behind these names.
Why Films?
Films are an interesting material for ultralight enthusiasts. They are lightweight, waterproof, and can be packed compactly. In their advanced form—such as cross-linked polyolefin films—they can compete with traditional outdoor fabrics in some areas but are significantly lighter and cheaper. Their tensile strength reaches values between 100 and 200 N/mm², placing them in the same range as traditional materials like Silnylon (30d), a commonly used material for tarps, etc. However, they weigh only half as much and are much more affordable. However, they are only superior in certain properties: tear and puncture resistance are generally lower than fabrics, which affects the repair requirements during a trip.
Polycro or Polycryo
The name "Polycro" or "Polycryo" likely originates from the ultralight hiking scene and refers to a thin plastic film often used as a groundsheet. The term probably derives from "polyolefin," the polymer family to which the material belongs, and "cryo" from cold, as the films were first used from window insulation films. The "cro" in Polycro likely comes from "cross-linked." Although the exact origin is uncertain, this name has become established in the scene.
Some special insulation films have a metallized layer (like aluminum) to reflect radiant heat. Others insulate by creating an air layer that reduces heat exchange through convection. What is actually being bought is unclear, and whether the film is cross-linked is never specified. This makes it difficult to compare the material.
Since these films are intended as temporary window insulation, they are usually not cross-linked. Cross-linking makes the material more robust and resistant to wear but would also make it stiffer. Cross-linked films are more often used in high-performance applications where durability and resistance to puncture or stretching are important.
Now, let's take a detailed look at the various types of films:
Cross-linked Polyolefin Films / Polycro / Polycryo
Material: High-quality, cross-linked polyolefin, usually multilayer.
Application: Ideal for demanding use in the ultralight sector. Whether as a groundsheet, tarp, or for other protective applications, these films offer an excellent strength-to-weight ratio.
Strengths: Very high tensile strength (100–200 N/mm²), cross-linked for added durability and longevity under mechanical stress.
Weaknesses: Tear and puncture resistance are lower compared to fabrics.
Repairability: Easy to medium—duct tape is often sufficient to permanently repair the film, depending on the thickness and structure of the film.
Tesa Moll / Window Insulation Films
Material: Polyethylene, occasionally polypropylene.
Application: Window insulation films are often used as a cost-effective alternative due to their lightness and waterproofness.
Strengths: Very light, waterproof, easy to source.
Weaknesses: Usually not cross-linked, limiting robustness. They are designed for minimal mechanical stress (applying to windows) and not for harsh outdoor conditions.
Repairability: Easy—can be easily repaired with duct tape.
Mattress Packaging (Hardware Store)
Material: LDPE (Low-Density Polyethylene).
Application: These packaging films are durable and waterproof but heavier and thicker than specialized outdoor films. They are often used as an inexpensive alternative.
Strengths: Very stable and durable.
Weaknesses: Too heavy and thick for the ultralight sector, especially compared to cross-linked films.
Repairability: Medium—can be repaired with sturdy duct tape, but the thickness of the film often poses a challenge.
IKEA Packaging Films
Material: LDPE or HDPE.
Application: Packaging from IKEA (e.g., for mattresses) is occasionally recycled by ultralight hikers and used as groundsheets.
Strengths: Very robust, tear-resistant, and water-repellent.
Weaknesses: Too thick and heavy for ultralight purposes. These films are designed to protect products where weight is not an issue.
Repairability: Medium—can be repaired with strong duct tape, but handling is more difficult due to the thickness.
Stretch Film (Pallet Wrap, more commonly used in the US)
Material: LLDPE (Linear Low-Density Polyethylene).
Application: This stretchable film is primarily used for wrapping pallets but also by hikers for lightweight protective covers.
Strengths: Very stretchy, light, and affordable.
Weaknesses: Low tear and puncture resistance. Not suitable for rough outdoor use.
Repairability: Difficult—since stretch film is very thin and stretchy, it is not easy to repair.
When is a Film the Right Choice?
Films are particularly suitable when weight is a critical factor and mechanical stresses are low. They offer excellent waterproofing and tensile strength at very low weight but are weaker in terms of puncture and tear resistance. However, they are very well suited as an ultralight groundsheet as long as the campsite is inspected for thorns, etc., beforehand. A sharp stone alone is not enough to cause damage. There are enough examples of thru-hikers who have completed the PCT without any damage to a film. Particularly cross-linked films today offer an impressive combination of strength and lightness but can be more sensitive than fabrics in extreme situations.
Repairability on the Trail
Cross-linked films can be easily repaired with tape, making them ideal for longer trips. Non-cross-linked films are usually less robust and require more frequent repairs. Unlike fabrics, film tears can often be quickly and permanently patched, as long as the material is not too badly damaged.
Conclusion
Films have established themselves as an interesting alternative in the ultralight and long-distance hiking sectors. They offer high tensile strength at minimal weight and are often cheaper than fabrics. However, their susceptibility to tears and punctures is a challenge that needs to be considered depending on the application and load. Cross-linked films lead the way in terms of performance, while window insulation and packaging films are simpler but less robust alternatives. However, it is important to note that every film has its place. If your current film or groundsheet serves its purpose, it makes sense to use it as long as possible instead of immediately switching to a new material. This article is not intended to criticize materials but to bring clarity to the confusing terminology.
Lastly, we want to point out that the information about the various materials (e.g., mattress packaging is made of LDPE) is based on our current knowledge and does not necessarily apply to all products on the market. Often, specific material designations are not provided, which is a significant disadvantage when evaluating and comparing films. This is an exciting topic, and we invite all readers to share their own experiences and opinions in the comments below.
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