Polyester ageing test for tent fabric
Background to polyester ageing test
A polyester ageing test, for many people, may be about as interesting as watching paint dry. The low ‘view rate’ of this post confirms this. However, the ageing property of tent fabrics is one of the most critical factors in the design of a DIY tent that will have a long service life in a harsh environment.
In a related post, I describe the success of my experimental polyester tent which is made of silver coated unwaterproofed polyester umbrella fabric. Against the predictions of the armchair experts, the shedding of rainwater was excellent. In that post, I discuss the excellent performance of the tent when compared with a similar tent that was made some 8 years earlier out of ripstop silnylon. The benefits were; no significant wet stretching, less condensation and more rapid drying for early-morning pack up.
I also had a hunch that the polyester fabric may even be more resistant to degradation by exposure to the elements. The survival of my crappy walking umbrella was the basis of this hunch and is backed up by the information on tent fabrics in this informative article; SlingFin Tent Fabric 101.
Mothy The Elder
The silnylon tent has had a lot of use by the time I came to compare it with the new polyester one. I speculated that the poorer performance of its fabric may be due to degradation from ageing and abundant use. I found a degraded sample of the silnylon on my washing line. It was an accidental test that happened because it was attached to some nylon tent guy cord that I had tied up on my washing line (and several campsites) to test the resistance of the cord to UV-degradation. I realised that continuous exposure to the elements could make an accelerated polyester ageing test and it could be used to assess the relative degradation rates of different tent fabrics.
I have made a small ageing test rig to hang samples of polyester and silnylon tent fabric and also my nylon and polyester cords. I am exposing them to the elements on my washing line. I think that the exposure testing should indicate if the polyester is worse, equivalent or better than the now well-accepted silnylon tent fabric.
I also thought that it might shed light (excuse the accidental pun) on the possible silnylon wetting-out and stretching problems for the aged silnylon that are described in the related post.
While this will be criticised by the few science Zelots, I hope the indications from this testing will allow me to anticipate the likely relative longevity of the polyester tent. I am not quite prepared to wait 8 years to find out.
Mothy The Elder
What will this rapid fabric ageing test that started on 14 September 2021 tell us?
Observations on 25 February 2022 (164 days exposure)
All test samples have survived 164 days of exposure to the elements. The most noticeable degradation is the fading of the blue colour of the polyester umbrella fabric on the side that is not silver coated. Luckily the blue side is on the inside of my tent and I think, as expected, the silver coating will provide great protection for the polyester beneath this reflective layer.
The polyester and nylon cords also show signs of fading. However, from past experience, the strength of the cord will be largely intact with this level of fading. For the photograph below I included some unexposed polyester cord, blue fabric, and nylon cord for colour comparison.
“Well, I did warn you that this would be about as interesting as watching paint dry.”
Update 11 January 2023 (484 days exposure)
Well, life is busy with skiing, fishing, tinkering, sailing paint drying and all those other chores. So here is an update on the ageing test, by popular request, “truthfully, it was only Cameron”. All the sun-exposed fabrics are showing obvious signs of colour fading as I anticipated. The structural integrity seems OK, but no formal strength testing has been done or the cutting open and examination of one of the sewn tubes of polyester and silnylon.
After 484 days of exposure to the elements, the mid-blue of the original polyester has become a rather pathetic light blue and the grey silnylon ripstop has faded significantly as have the yellow nylon and polyester cords.
The silver coating on the blue polyester umbrella fabric is holding up well and I expect that the polymer that is protected within the reflective coating will be largely undamaged (as would be the case when I use the silver coating on the outside of the tent).
Given that the polyester umbrella fabric can survive 320 of exposure to the elements, this would seem to be yet another reason to use this wonder fabric for making low-cost backpacking tents from it. The tents can be; dry, low-condensation, stretch-free, fast-drying/de-icing, durable and look great for a long time. The silver coating appears to be critical to durability and should help retain heat in winter and reflect heat in summer.
Update 27 January 2023 (500 days exposure)
The previous updates were just visual observations, it was time to test some aged strips to destruction. I suspended a bucket on a polyester test strip that had been exposed for 500 days. I progressively added ~2,000g jug loads of water to the bucket to find the breaking point. The polyester strip broke with a load of about 8,000g (4 jug full). The total load was about 9,000g when the weight of the bucket was included.
I realised that this measurement needed more context, so I did the same test to the equivalent silnylon test strip (grey silnylon) that had been exposed for the same duration. It started to fail with only one jug full and failed completely with the start of the second load (estimated total load including bucket 3,000g.
This meant that after 500 days of exposure, the polyester was about 3 times stronger.
Holding a load of 9,000g sounds pretty good but I thought it needed even more context, so I hurried upstairs to my sewing machine and made another test strip from unexposed polyester. The new polyester withstood a load at least 14,000g* (7 jug loads) and I finished testing, thinking that was a reasonable test load.
Note*. I subsequently found that it could support a load greater than 40,000g
Here is a little video of the strength testing after 500 days of exposure.
Having ripped a polyester test strip during load testing I cut it open with scissors to reveal the preservation of the polyester fabric colour within the protective silver coating. The colour was similar to a sample of the unexposed fabric. This shows that the silver coating protects the fabric to a large extent.
Even with this silver protection, the polyester strength has deteriorated significantly with 500 days of exposure.
Conclusion & discussion
I think it is safe to conclude that silver-coated polyester has superior ageing properties when compared to silnylon. The silver coating protected the polyester from fading and probably contributed to the polyester’s much higher strength after 500 days of exposure (Please see Addendum 1).
The decay of the polyester fabric is still interesting. The silver coating reflects the majority of visible radiation but not all of it. The unreflected radiation is probably the cause of the decay of the silnylon fabric’s strength. The natural sunlight inside a silver-coated polyester tent is much dimmer than for an equivalent silnylon one. However, the view from the inside of a tent made from silver-coated polyester (photo below) shows that sunlight is substantially getting through the silver coating and the polyester. This small amount of radiation penetration is probably the cause of the loss of strength over the 500-day exposure period.
Along with low condensation, low wet stretching and fast drying, this ageing test shows that superior longevity can be added to the advantages of silver coated polyester over silnylon for making backpacking tents if the silver coating is arranged to face the sun (as in the above testing).
On the other hand, when the polyester samples had the silver coating on the inside (As described in Addendum 1.), The decay of the polymer was as bad, if not worse than the sinylon. This indicates that the silver coating has probably been highly protective of the polyester fabric. Probably silver coating would be desirable for all such tent fabrics for this reason.
Addendum 1
Having speculated about the silver coating possibly providing UV protection to the silver-coated polyester umbrella fabric, I realised that I had the inside-out test sample still on my washing line on March 10 2023.
So I hastily prepared to load test it. While settling the test rig down with an empty (~1kg) bucket suspended from the sample I estimate that I applied an extra one or two kg load to the bucket and the fabric started to rip. It was very weak and I think I could safely conclude that the silver coating was the major contributor to the superior survival of the polyester when it was used as a sun shield. This also confirms the wisdom of my decision to put the silver coating on the outside of my tents.
Tim
Note: I have now tested the relative strength of polyester and silnylons when they have been stored out of direct sunlight and the relative leakage of water through both fabrics with a hydrostatic head of about 500mm of water. Polyester continues to come out on top!
ADDENDUM 1
The summary table below may help to better summarise the tangled mess of my tent fabric and cord testing for backpacking tents.
Nylon and polyester strength after extended sun exposure
| Table 1. Breaking loads of various tent fabric samples and cords before and after extended sun exposure. Also subjective assessment of the performance of the materials for backpacking pyramid tent. The fabric test samples were sewn tubes of fabric that were 30mm wide. The samples were supporting a suspended bucket/s to which 2L jug loads of water was added. The weights shown (~kg) included the tare weight of the bucket/s and were based on the equivalence of one litre of water=one kg | |||||
|---|---|---|---|---|---|
| Sample type | Polyester umbrella fabric silver coated | Silylon ripstop fabric 1 (grey) | Silylon ripstop fabric 2 (orange) | Polyester cord (brickies line, yellow) | Nylon cord (brickies line, yellow) |
| Material property | |||||
| Estimated material weight | ~57gsm | ~37gsm | ~37gsm | xx/m | xxg/m |
| Fabric strength in as-new condition (breaking load kg) Post link | >40kg | ~38kg | ~16kg | 38kg | 38kg |
| Fabric strength after 500 days of weather exposure (breaking load kg) Post link | ~9kg | ~3kg | NA | NA | NA |
| Fabric strength after 540 days of inside-out exposure Post link | ~3kg | NA | NA | NA | NA |
| Cord strength in as new condition before weather exposure (breaking load kg) Post link | NA | NA | NA | 38kg | 38kg |
| Cord strength after 540 days of exposure Post link | NA | NA | NA | 19kg | 29kg |
| Other performance characteristics | |||||
| Fabric permeability to prevent tent condensation | Good | Poor | Poor | NA | NA |
| Fabric resistance to wet stretching | Excellent | Poor | Poor | not yet tested | not yet tested |
| Speed of drying for cold morning pack ups Post link | Excellent | Poor | Poor | NA | NA |
| Bond strength when glued with silicone rubber. [Add post link when available] | Very poor | Good | Excellent | ||
| Fraying/unraveling [Add post link when available] | NA | NA | NA | Poor | Good |
| Simple knot holding [Add link when available] | NA | NA | NA | Poor | Good |
| The meaning of life [Add post link when available] | NA | NA | NA | NA | NA |
OTHER POSSIBLY MORE INTERESTING POST FOR PYRAMID TENT FANS
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DIY silicone seam sealer- Getting a long pot-life
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Tie out tabs for pyramid tents- Keeping DIY tabs cheap, small, simple, strong and light
A pyramid tent vestibule- Turn a pyramid into a winter palace, using a spreadsheet model
