Direct answer: Elevated temperature and prolonged UV exposure both reduce the strength of a polyester lifting sling, but they do so by different mechanisms and on different timescales. Heat above a fibre-specific limit causes permanent loss of strength, which is why EN 1492-1 assigns a maximum working temperature to polyester webbing. Extended sunlight causes UV degradation of the polymer, a slow, cumulative weakening that is invisible at first. Strength after either exposure cannot be assumed, so the safe approach is to work within the temperature range the standard allows, to keep slings out of unnecessary sunlight, and to withdraw slings showing heat or UV damage.

Two Different Threats to the Same Fibre

It helps to separate the two. A temperature event is usually acute: a sling touches a hot pipe, or is used near a furnace, and the fibre is affected within seconds or minutes. UV degradation is chronic: a sling stored on an open site for months slowly loses strength without any single event. Both end in a weaker sling, but the inspection signs, the timescale and the prevention measures differ, so they should be managed separately in any lifting regime.

Temperature: What the Standards Allow and Why

Man-made fibres each have a working temperature range, and the standard for polyester webbing slings sets the limit that applies to slings of that material. EN 1492-1 states a maximum working temperature for polyester flat woven webbing, and this figure should be read as the ceiling for safe, repeated use — not a target to operate at. Above the limit, polyester does not simply get "a bit weaker"; it can soften, and in a severe contact event such as molten splash or a hot metal edge, it can melt or char outright.

The practical consequence is that a polyester lifting sling is the wrong choice for hot work unless the temperature at the sling can be kept within its rated range. Where heat cannot be avoided — near ovens, foundries or heat exchangers — the options are to insulate the sling from the source, to use a sling type rated for higher temperatures, or to redesign the lift so the sling never contacts the hot surface. Claims about specific temperature ceilings should always be taken from the standard or the manufacturer's verified data for the exact sling, not from general rules of thumb.

What Heat Actually Does to Polyester

Polyester is a thermoplastic fibre, which is why temperature matters so much. At moderate heat it may gradually lose some tenacity; at higher temperatures it can shrink and stiffen, and a localised hot point can fuse yarns together. Any of these changes reduce the load the polyester lifting sling can safely carry, and they are not reversible. Where a polyester lifting sling has been in contact with a hot surface, the affected region should be inspected for glazing, charring or stiffening, and the sling withdrawn if any is present. The dangerous cases are often small: a weld spatter burn, a brief touch on a hot exhaust, or a sling left against a heated surface during a break.

UV Degradation and Additive Protection

Ultraviolet light from the sun attacks the polymer chains in textile fibres, and the effect accumulates over hours of exposure. Polyester is more resistant to UV than some fibres, and manufacturers commonly add stabilising additives to improve outdoor durability, but no textile sling is immune. The practical signs are fading, a chalky surface, stiffening and, eventually, loss of strength that is not visible at all. Where a polyester lifting sling is used or stored outdoors, limiting direct sun exposure and inspecting for surface change is the main defence. Keeping a polyester lifting sling in a closed, shaded store when it is not in use costs nothing and can add measurable life in a sunny climate.

Exposure, Inspection Focus and Action

The table below links common exposure conditions to what an inspector should look at and the action to consider. The decision to withdraw a sling follows the removal criteria in the applicable standard; this table is for organising inspection and prioritising attention.

Storage and Handling to Limit Both

Much ageing is preventable with simple storage discipline. Slings should be kept clean and dry, away from direct sunlight, heat sources and chemical vapours, and hung or laid flat so they are not crushed or kinked. Indoor storage with a stable, moderate temperature is the goal. Rotating stock so older slings are used before newer ones prevents a sling from ageing unused on a shelf, and keeping slings in a dedicated store rather than draped over equipment removes the daily dose of sun and heat that slowly erodes strength.

Frequently Asked Questions

Can polyester slings be used outdoors at all?

Yes, and manufacturers use stabilising additives to improve UV resistance, but prolonged direct sunlight still causes cumulative ageing. Use slings outdoors within their rated temperature range, store them under cover, and inspect regularly for surface change.

Is a faded sling unsafe?

Fading indicates UV exposure but does not by itself prove a loss of strength. It is a prompt to inspect more closely and to consider the exposure history; where the sling has spent long periods in strong sunlight, conservative replacement is reasonable.

What is the working temperature of a polyester sling?

It is set by the applicable standard and the specific product, and should be taken from verified data for that sling. Operating near the ceiling reduces margin, so where heat is present, treat the limit as a boundary to stay well inside, not to reach.

Does a higher design factor protect against heat damage?

Design factor provides margin against variability and wear; it does not make the fibre heat-proof. A sling exposed above its temperature limit should be assessed against the removal criteria regardless of its design factor.

Practical Guidance for Buyers and Rigging Engineers

• Confirm the rated temperature range for the exact sling and keep the working environment inside it.
• Where heat is unavoidable, insulate the sling or choose a sling type suited to the condition — an example is this high-temperature-resistant 2 t endless webbing sling — and verify the rating for your actual temperature.
• For outdoor use, favour a stabilised, UV-resistant option such as this heavy-duty polyester sling offering enhanced UV resistance, and still store it under cover.
• Store slings dry, shaded and away from heat and chemical vapours; rotate stock so slings are not aged by long storage.
• Inspect for fading, glazing, charring and stiffening, and treat any heat event as a reason to withdraw and assess.

Heat and sunlight are slow, quiet adversaries: neither produces the drama of an overload, yet both steadily eat into a sling's strength. Managing them is mostly a matter of discipline — respect the temperature range, shield the sling from the sun, store it properly, and inspect for the tell-tale surface changes that say ageing has begun.