Polyester vs. Nylon Flat Slings: Chemical Resistance and Elongation Profiles

A chemical plant needs a flat sling for lifting stainless steel components in an environment where acid fumes are present. A marine repair facility needs a sling that can handle hydraulic oils and seawater exposure. Both operations require synthetic flat slings—but the right material choice is different for each.

Lishenflex has been manufacturing synthetic flat slings for over two decades, and one question we hear frequently is: Polyester or nylon—which is the better choice? The answer is rarely simple. According to Wikipedia's entry on polyester, polyester is a category of polymers valued for its durability, chemical resistance, and low moisture absorption. Wikipedia's entry on nylon explains that nylon is valued for its strength, elasticity, and abrasion resistance. Both materials make excellent lifting slings, but they are not interchangeable . According to the Canadian Centre for Occupational Health and Safety (CCOHS) , nylon slings are damaged by acids but resist alkalis, while polyester slings are damaged by alkalis but resist acids . The key is matching the material to the environment.

Chemical Resistance: The Critical Safety Difference

The most important distinction between polyester and nylon flat slings is their chemical compatibility. Choosing the wrong material for a chemical environment can lead to catastrophic failure—often without visible warning.

According to Liftex's material comparison guide, the key chemical resistance differences are :

Source: Liftex; CCOHS; CERTEX Denmark

CCOHS confirms that nylon is subject to degradation in acids ranging from none to total degradation, while polyester is resistant to many acids but damaged by alkalis . CERTEX Denmark adds that solutions of acids or alkalis that are harmless at low concentrations can become concentrated through evaporation and cause damage .

Critical safety warning: Chemical damage to synthetic slings is often invisible . The fibers weaken internally while the sling appears normal on the surface. According to Empire Rigging, chemical damage is often invisible—the fibers weaken internally while the sling looks perfectly normal on the outside, which is why knowing your environment matters before you choose your material .

Acid Environments—Choose Polyester

When lifting in environments with acid exposure—chemical plants, battery manufacturing, metal finishing, paper mills—polyester is the correct choice. Nylon, by contrast, is destroyed by acids. Mazzella Companies notes that nylon is subject to degradation in acids ranging from little to total degradation, while polyester is resistant to many acids . The NSRP Ship Production Rigging Guide warns that hydrochloric and sulfuric acids, even in diluted form, can cause significant loss of strength in nylon .

Alkali Environments—Choose Nylon

When lifting in environments with alkali exposure—caustic cleaning solutions, concrete manufacturing, certain chemical processing—nylon is the better choice. Polyester is damaged by alkalis, while nylon is virtually immune to the effect of alkalis . The UNIROPE fiber properties guide notes that nylon has good resistance to aldehydes, hydrocarbons, ethers, and some alkalis .

Elongation Profiles: Stretch Under Load

The second major difference between polyester and nylon flat slings is elongation—how much the sling stretches when loaded.

Liftex provides the following elongation data :

Source: Liftex; UNIROPE

Polyester—Precision and Stability

Polyester's low elongation (3–4% at rated load) makes it the preferred choice for :

• Precise load positioning—minimal stretch means better control

• Low-headroom applications—less vertical space consumed during lift

• Loads that cannot tolerate bouncing or swinging

• Operations requiring stable, predictable lifting

Empire Rigging provides a practical example: lifting a 20-foot load with a nylon sling that stretches 10% results in roughly two feet of elongation, while a polyester sling would stretch only about seven inches . In tight overhead spaces, that difference matters.

Nylon—Shock Absorption and "Forgiveness"

Nylon's higher elongation (6–10% at rated load) provides :

• Shock absorption—the material "gives" before taking full force

• Dynamic loading tolerance—better for loads that shift during lifting

• Forgiveness over irregular hardware—nylon is more forgiving if subjected to bunching and placement over irregular hardware shapes

• Enhanced operator safety margin—the stretch absorbs sudden loads

According to Liftex, nylon's higher stretch acts as a shock absorber, making it the preferred choice when loads may shift or when dynamic loading is a concern .

Moisture and UV Response

Moisture Effects

Nylon is hygroscopic—it absorbs moisture from the environment. According to the NSRP Ship Production Rigging Guide, nylon loses 15% of its strength when wet . Liftex and CCOHS confirm this, noting that nylon slings can lose 10–15% capacity when wet . Strength is restored upon drying, but the sling should not be used at rated capacity when wet.

Polyester does not absorb water and suffers no strength loss when wet . This makes polyester the preferred choice for :

• Marine and offshore applications

• Outdoor lifts in wet conditions

• Environments with high humidity

CERTEX Denmark notes that Dyneema® does not absorb water, unlike other materials such as polyester and polyamide .

UV Resistance

Polyester offers superior UV resistance compared to nylon . Nylon fibers are affected by UV rays and sunlight, resulting in considerable strength loss over time . Mazzella Companies warns that environments in which synthetic web slings are continuously exposed to ultra-violet light can affect the strength of synthetic webbing in varying degrees, from slight to total degradation, and that degradation is cumulative . For slings used outdoors or in direct sunlight, polyester is the more durable choice.

Temperature Limits

Under EN 1492-1, both polyester and nylon flat slings are suitable for use and storage in the temperature range -40°C to 100°C . This applies to both materials. However, Empire Rigging notes a practical difference in continuous use limits: nylon is rated up to 194°F (90°C), while polyester is rated up to 180°F (82°C)—slightly lower . Above these temperatures, the materials begin to lose strength.

Critical note: In a chemical environment, these temperature ranges may vary, and the advice of the supplier should be sought .

Identification: How to Tell Polyester from Nylon

ASME B30.9 and WSDA-WS-1 require that every web sling has a permanently attached tag stating the material . In addition, polyester slings have a blue identification line woven into the webbing—if you see the blue line, it is polyester . Nylon slings do not have this identification line. The color-coding system under EN 1492-1 applies to both materials equally.

Selection Guide

Summary and Practical Recommendations

Polyester and nylon flat slings both offer excellent strength and durability, but they are not interchangeable. Choosing the wrong material for your environment can lead to hidden degradation and sudden failure.

Key takeaways:

1. Acid environments = Polyester—nylon is destroyed by acids

2. Alkali environments = Nylon—polyester is damaged by alkalis

3. Precision lifts = Polyester—low elongation provides control

4. Dynamic loads = Nylon—higher stretch absorbs shocks

5. Outdoor/wet = Polyester—UV-resistant and moisture-resistant

6. Check the blue line—polyester slings have a blue tracer line; nylon does not

7. Always verify the tag—ASME B30.9 requires material identification on the sling tag

Lishenflex manufactures both polyester and nylon flat slings to EN 1492-1 and ASME B30.9 standards, with clear material identification and color-coded capacity markings. We offer guidance on material selection based on your specific chemical environment and application requirements.

If you need assistance determining whether polyester or nylon is the right choice for your lifting operation—or need help identifying the appropriate sling for a chemically active environment—please send an email to sales@lishenflex.com, and our technical team will provide one-on-one support.