Exposure Resistance + Care

Exposure Resistance + Care of Bike Bag Fabrics

Exposure Resistance is our #6 ranked bike bag fabric property in terms of our estimate of its importance to the majority of bikepackers and cycle tourists. While exposure resistance is not a top-of mind concern typically, it is very important to the long term reliability of a bike bag. For some folks going on extended tours, this property can be one of the highest priority.

In this guide, we break down these environmental forces into the following exposure types: UV, Moisture, Microbial, Particulates, Chemicals, Heat and Cold. Fabrics that resist and minimize the impacts of exposure to the environment are of course what bikepacking and cycle tourists are looking for in the fabrics used in their bike bags.

A fabric’s exposure resistance is closely connected to other critical fabric properties, durability, water resistance, appearance and structure. Each of these fabric properties can degrade due to the various exposures that we will cover in this guide.

The durability property, which is our #1 ranked fabric property, covers the most important type of exposure to fabric, physical force. Please see our durability guide to compare durability to the exposure types covered in this guide. Very briefly, physical force exposure covers the abusive impacts caused by various forms of physical abrasion and wind.

While it is helpful to consider the impact of each type of exposure on its own, in most cases, the degradation of fabrics is a result of combined exposures working together and sometimes multiplying their power to degrade fabric. At the conclusion of this guide, we present some the most common and impactful combination of exposures.

The majority of exposure types that we are examining in this guide impact fabrics through long-term exposure. Short-term exposures are typically only relevant to physical (durability) and microbial exposure, which can have rapid near term negative consequences: tears and puncture, mold and mildew. Beyond those short term disasters, in the exposure resistance property we are mostly considering the more gradual deterioration of fabrics over time due to ongoing use and abuse.

UV Exposure

Within the other, non-physical exposures covered within this guide, we regard UV exposure as typically having a more persistent and troublesome impact on bicycle bags than the other types of environmental exposure. Moisture, Microbial, Particulates, Chemicals, Heat and Cold are in general much more occasional concerns connected to atypical usage, extreme conditions or as a result of various mistreatment of bike bags.

The power of our sun, endless radiation streaming down on our planet, giving us life and warmth, but also beating down ceaselessly, gradually breaking down materials. Long-term usage of bicycle bags whether on extended bicycle tours, frequent short bikepacking trips or regular commuting will lead to a significant amount of the sun’s ultra violet (UV) radiation exposure over time. Riding in sunny climates and at high elevations will amplify the impacts of UV exposure. Extended UV exposure will seriously degrade all fabrics to varying degrees. Fabrics with strong UV resistance can slow down the speed of this degradation, significantly extending the life of a bike bag.

UV Exposure’s Fabric Degrading Processes

Extended UV exposure deforms and erodes away at fabric’s fibers, coatings and the adhesive bonds between laminate layers through several chemical processes.

Photodegradation: This process breaks down the chemical bonds within polymer chains leading to a reduction in molecular weight and changes in mechanical properties.
Oxidative Degradation: The free radicals produced during photodegradation react with oxygen in the environment, forming peroxyl radicals and hydroperoxides. This leads to a chain reaction of radical formation and polymer breakdown. The oxidative degradation further weakens the polymer chains by continuing to break bonds, reducing molecular weight and mechanical properties.
Crosslinking and Embrittlement: During UV exposure, some polymer chains may form crosslinks, where new bonds are created between chains. Initially, this can increase the rigidity and thermal stability of the material. However, excessive crosslinking can lead to embrittlement making the polymer less flexible and more brittle. As oxidative degradation continues, the material becomes increasingly brittle, leading to cracks and fractures under mechanical stress.

The Impacts of UV Exposure on Fabric Properties

Fabrics are negatively impacted in a variety of ways due to extended UV exposure.

Reduced Durability: UV exposure weakens the tensile strength, tear strength, and abrasion resistance of fabrics by degrading the fibers, which makes them less capable of withstanding mechanical stresses and wear. When UV exposure deteriorates surface coatings, the coating’s additive protective capabilities are diminished leading to increased wear and tear on the fabric. With laminated fabrics, when adhesive bonds between laminate layers are weakened by UV exposure, delamination further compromises the fabric’s structural integrity and durability.
Reduced Water Resistance: UV exposure reduces the water resistance of fabrics by degrading the surface coatings, making the fabric more susceptible to water penetration. The fibers themselves can become more absorbent, allowing water to penetrate more easily. In laminated fabrics, UV exposure can weaken the adhesive bonds between layers, causing delamination, which compromises the fabric’s ability to repel water effectively.
Degraded Appearance: UV exposure alters the appearance of fabrics by causing discoloration, fading and shifting the color, and coarsening the surface texture, making it rougher. In coated fabrics, UV exposure can alter reflective finishes into matte finishes. Additionally, flaking and peeling of coatings caused by UV exposure reduces the fabric’s aesthetics. In laminated fabrics, UV exposure weakens the adhesive bonds between layers, leading to delamination and disruption of the fabric’s uniform appearance.
Altered Structure: UV exposure causes fabrics to become more rigid as the fibers lose their flexibility and become brittle. Additionally, UV exposure reduces the fabric’s elasticity, making it less stretchable and more prone to losing its shape after being stretched. In laminated fabrics, UV exposure weakens the adhesive bonds between layers, leading to changes in the stability between laminate layers with less cohesive movement between.

UV Resistance Factors

The level of UV Resistance of fabrics is a result of multiple factors. Quantifying each factor’s contribution to a fabric’s overall UV resistance is difficult without highly controlled studies. Most fabric tests for UV resistance are only for a specific fabric, though generally with the variable included of the fabric’s various colors. Even without multi-variant fabric testing results, considering all of the factors at play will still help us gain a better understanding of what fabrics will likely have better UV resistance over other.

We break down the contributing factors while offering our approximated ranking order of their importance to the UV resistance of bicycle bag fabrics.

Fiber Type:
- Nylon: Moderate UV Resistance
  Prolonged exposure to sunlight can cause degradation, leading to a reduction in tensile strength and color fading over time.
- Polyester: High UV Resistance
  Polyester maintains its durability and color stability longer when exposed to UV radiation, making it a preferred choice for outdoor applications where prolonged sun exposure is a concern.
- UHMWPE: Excellent UV Resistance
  UHMWPE retains its structural integrity and mechanical properties even after long-term exposure to sunlight. It is highly durable and less prone to degradation from UV radiation, making it ideal for demanding outdoor applications.
- XPac: Very High UV Resistance
  Known for its UV resistance, XPac’s multi-layered construction, which includes a polyester face fabric and additional protective layers, provides superior protection against UV radiation, ensuring longevity and performance in harsh outdoor environments.
- EcoPak: Very High UV Resistance
  EcoPak, another advanced composite fabric, offers very high UV resistance. Like XPac, it features a multi-layered design that enhances its durability and resistance to UV-induced degradation, making it a reliable choice for bike bags and other outdoor gear exposed to the elements.
Fabric Construction: Tighter, smoother weave patterns leave less outer surface area for UV rays to impact. Thicker fabrics are inherently more UV resistant with UV unable to penetrate deeper into the fabric. Fabric constructed from multiple laminate layers will benefit from the UV resistant properties of the outer fabric.
Coatings: Protective coatings applied to fabrics can significantly enhance their UV resistance by reflecting or absorbing UV rays. The same coating used to increase water resistance also have UV protective properties.
Color and Dyes: Darker colors and UV-stabilizing dyes improve UV protection by absorbing more UV radiation and reducing the rate of degradation.

**UV absorbers and stabilizers can be incorporated into fibers, coatings and dyes to further enhance their ability to withstand UV radiation.

UV Testing

A variety of testing procedures are utilized by fabric and bike bag manufacturers to measure the UV resistance level of fabrics. These tests involve comparing the appearance and color of fabric samples before and after the test, assessing for fading, discoloration and structural degradation to the fabric. Additionally, fabric durability tests are often deployed after the use of accelerated weathering and outdoor exposure testing to test how various aspects of durability are impacted by controlled levels of UV exposure.

Accelerated Weathering: These tests simulate continuous sunlight exposure onto fabric samples in a controlled environment to assess UV resistance.
ASTM G154: Uses a fluorescent UV lamps in an exposure chamber to simulate the effects of sunlight. It is commonly deployed because of its cost-effectiveness and practicality.
ASTM G155: Uses a Xenon Arc lamp in an exposure chamber to simulate full-spectrum sunlight, including UV, visible, and infrared light, providing a more accurate representation of actual sunlight exposure. Due to the complexity and cost of the equipment, this test is typically reserved for fabric testing requiring more precise sunlight simulation.
Spectrophotometric Analysis: These tests measure the amount of UV radiation absorbed or transmitted through the fabric. By analyzing the fabric’s UV absorbance spectrum, one can infer its UV blocking capabilities and resistance.
ASTM E1347: Measures the color and color differences of fabrics using tristimulus colorimetry, which quantifies colors based on three primary color values. This process provides precise data on the fabrics’ color consistency, stability, and resistance to fading when exposed to UV light.
Outdoor Exposure: In these tests fabrics are exposed to natural sunlight and environmental conditions for extended periods. This real-world testing helps assess how fabrics withstand UV exposure in actual usage scenarios. The results are compared with control samples kept in dark storage.
ASTM D1435: Provides guidelines for exposing fabrices to natural weathering conditions over an extended period. This test assesses the durability, color stability, and overall performance of these fabrics when subjected to real-world environmental factors like UV radiation, moisture, and temperature fluctuations.

UV Exposure Prevention & Care

With the unavoidability of significant UV exposure during long distance bicycle travel, taking extra care of the fabrics of bike bags can reduce the level of impact.

Storage: While on extended bicycle tour, being thoughtful about where you park your bike, can really add up over the duration. When stopping for more than 15 minutes, finding a shady spot for your bike will not only help reducing UV exposure, but also helps to keeps your food and water cooler.
Cleaning: Combining the forces of microbials, particulates and/or chemicals with UV exposure can substantially accelerate a bike bag’s fabric degradation. Regular cleaning with soap and water will reduce the potential for these multiplying factors.
Aftermarket UV Protective Coatings: A variety of available spray-on, brush-on and wash-on products can be used to add an additional UV protective layer to fabrics while also increasing their water resistance. These coatings vary in their ability to adhere to and work well with different types of fabrics and fabric coatings. Be sure to research which coating will work best with your bike bag’s fabric. For consistent protection, these coatings typically should be reapplied every 3 to 6 months or after thorough washing or other similar exposure. A great use case for these protective sprays are for preparing bike bags made of nylon fabric, known for more moderate UV resistance, for an extended bicycle tour.
Example Products:

Moisture Exposure

When we talk about moisture, we are talking about the long-term impacts of water on the fabrics used in bicycle bags. Real-time resistance to water penetration is a very important fabric property on its own, in fact Water Resistance is our #2 ranked fabric property. In our examination of long term moisture exposure, we’re focused on how a fabric degrades due to consistent water exposure over an extended period of time. And naturally, a fabric’s ability to avoid the negative impacts of long-term moisture is strongly correlated to its water resistance.

Beyond penetrating and/or absorbing into fabric through a farbic’s inability to resist water, there are other ways moisture can get inside a bike bag and slowly degrade the fabric. Wet items might be stored inside, water bottles leak or water gets in through the bag’s openings. Moisture levels are also increased in humid environments.

However moisture gets to the fabric, long-term exposure will slowly degrade it in a variety of ways. Short-term exposure to moisture is typically not a big problem. Thoroughly dry your wet bags out after a wet weekend romp and their should be little to no consequence. Frequent and long-term moisture exposure is the concern here and there is certainly plenty of opportunity for this to happen during a long distance bicycle tour especially through wet climates or regular bicycle commuting in rainy weather.

We’re also distinguishing long-term moisture exposure from microbial exposure. While microbial exposure is dependent on moisture exposure, it is helpful to separate them out as their impact and prevention are two distinct topics.

Moisture’s Fabric Degrading Processes

Long-term moisture exposure degrades fabric’s fibers, coatings and the adhesive bonds between laminate layers through the following chemical processes.

Hydrolysis: This process occurs when water molecules penetrate the material and interact with the chemical bonds within the polymer chains, such as amide bonds in Nylon and ester bonds in polyester. This interaction causes these bonds to break down, converting them into new compounds like carboxylic acids and alcohols. Over time, this breakdown leads to a reduction in the length and integrity of the polymer chains.
Oxidation: This process occurs when moisture and oxygen initiate chemical reactions with the polymer chains. This exposure leads to the formation of free radicals that attack the polymer chains. Over time, these free radicals cause the polymer chains to break down through on-going oxidative reactions.
Leaching of Additives: This process occurs when moisture penetrates the fabric and dissolves the chemical additives, such as stabilizers, plasticizers, and UV inhibitors, that are incorporated into the material. These dissolved additives are then carried away from the fabric by the water. Over time, this process depletes the fabric of its essential chemical additives, altering its composition.
Chemical Swelling and Shrinking: This process occurs when moisture is absorbed, causing the polymer chains to expand and increase in volume. As absorbed water evaporates, the polymer chains contract and decrease in volume. Repeated cycles of wetting and drying cause polymers to continuously swell and shrink.

The Impacts of Moisture Exposure on Fabric Properties

Fabrics are negatively impacted in a variety of ways due to extended exposure to moisture.

Reduced Durability: Long-term moisture exposure reduces the durability of fabrics by causing chemical degradation in fibers, weakening their structural integrity and mechanical properties like tensile and tear strength. Coatings on the fabric can degrade, losing their protective and water-repellent properties. In laminate fabrics, moisture weakens the adhesive bonds between layers, leading to delamination and compromising of fabric’s composite strength.
Reduced Water Resistance: Long-term moisture exposure reduces the water resistance of fabrics by degrading their coatings, leading to a loss of their water-repellent properties. In laminate fabrics, moisture weakens the adhesive bonds between layers, causing delamination and compromising the integrity of the water-resistant barrier.
Degraded Appearance: Long-term moisture exposure degrades the appearance of fabrics by causing coatings to peel, crack, or flake off, leading to an uneven and worn look. The fibers themselves can swell and shrink with repeated wetting and drying cycles, resulting in fabric distortion and texture changes. In laminate fabrics, moisture weakens the adhesive bonds between layers, causing delamination that creates visible bubbles or separation lines. These combined effects result in a visibly aged, damaged, and less aesthetically pleasing fabric.
Altered Structure: Long-term moisture exposure causes fabrics to become less flexible as fibers swell and shrink with repeated wetting and drying cycles, leading to increased rigidity and reduced stretchability. In laminated fabrics, as moisture weakens the adhesive bonds, delaminated layers lose cohesion.

Moisture Resistance by Fiber Type

Long-term moisture resistance of fabrics is first and foremost a factor of a fabric’s ability to resist water penetration and absorption all together. Please see our fabric’s water resistance property to see our thorough examination of what increases this property, which includes a fabric’s fiber type, coatings, construction and adhesive bond strength (in laminated fabrics).

Here we compare the ability of different fabric fiber types to withstand long-term moisture exposure when water manages to penetrate and absorb into it for long periods of time.

Exposure Resistance + Care