Strip washing results – part 2

An analysis of the results of further tests on nappies INOSW

March 2016


This report follows on from the blog post which was published by Ellen Young on February 16th here and while some small repetition of her excellent work is inevitable I advise that you read her post prior to this in order to get a more complete picture of the process that we have been through. I will not be explaining how the nappies were selected or going over ground which she has already covered and, as such, this piece of work does not stand alone.
Quick Summary

Jenny Macintosh was sent a number of nappies collected from the NSG which were considered to be INOSW. She selected the most appropriate candidates through a procedure which is detailed here. An additional nappy in the form of a Totsbots V3 with extremely poor absorbency was added to the group and they were sent to Shirley Technologies Ltd for analysis.
Initially Shirley Tech only tested nappy D and the TB V3 (Nappy B). The results of the analysis of these two nappies and a control sample were revealed on the day of the lab visit and were discussed on the chat here and on a post on the NSG page by Kirstine Anderson on the 6th of February and through the blog post detailed above.
After further clarification of the brief, Shirley Technologies Ltd agreed to test the remaining 3 nappies and these more complete results are what we present to you today. In total there were 5 candidate nappies tested and one control nappy.


Brief Analysis of the results

Shirley Technologies Ltd produced an updated report 407322-test-report and I have  attempted to collate the information within it into an easy and digestible form. We did not provide the Lab with the washing histories of the candidate nappies and I have drawn that information and the results from the tests together to enable more complete analysis. There are a few paragraphs from the Lab report which I believe are important and I have reproduced them in order to more easily draw some conclusions.
There were 3 tests undertaken.
1. Solvent extraction and Infrared Spectroscopy
2. Bioburden
3. Ash content

STL was also able to make some conclusions as a result of the tests that were undertaken

1. Comments on Solvent Extraction
STL considered that the values obtained by quantifying the extractable matter contents of all the nappies were nominally and statistically similar.
More importantly STL’s significant experience of similar analyses in the past leads to the comment that the amounts of extractable material are low. Most significantly, the quantified amounts are not dissimilar to what STL would consider might be expected to be found on a new nappy…..STL would comment that only the presence of alkyl benzyl sulphonate on some of the nappies indicates the presence of a detergent residue .
Thus STL would offer the initial conclusion that it does not appear to be the presence of a non-solvent soluble residue (i.e. and oil) on the nappies which is deteriorating their function.

2. Bioburden
…STL considered that the values obtained by quantifying the bioburden of the majority of the used nappies were nominally and statistically similar.
However STL would note that nappy “G” exhibited a Bioburden 10x higher than all the others. STL would comment that this difference is likely due to variations in usage factors and more significantly, the cleansing routine(s) that this nappy has undergone…
Even in the light of the difference exhibited by nappy “G”, STL’s significant experience of similar analyses in the past leads us to comment that all the Bioburden values are high and indicate significant residual soiling of the used nappies.
Given the fact that these nappies were reported to have been cleansed multiple times, it is the comment of STL that these washing procedures must have been performed at a temperature so low as to not give a sterilising effect….

3. Ash Content
…STL considered that the values obtained by quantifying the ash contents of the used nappies were dramatically different.
STL’s significant experience of similar analyses in the past leads to the comment that the ash contents of the nappies “B” and “G” is in line with what might reasonably be expected for a product of this type… By contrast, the ash contents of nappies “D” and “E” is far higher than STL would reasonable expect for a product of this type. STL subsequently analysed the nature of the residue from the ash content on these nappies and found it to contain hydroxyl apatite – a hydroxylated calcium phosphate. Further analysis showed that this material was intimately associated with the fibres of the nappy fabric, and formed a skeletal residue when the ashing removed the cellulosic fibre.
STL would comment that this hydroxyl apatite is a common by-product of insoluble components of detergents re-depositing onto washed materials of cellulosic composition. This effect is known to be exacerbated by the presence of calcium or magnesium salts in the water, as such the effect is more prevalent in so called “hard water” areas of the country. Obviously the effect is also exacerbated by the frequency and number of washes performed on a material, so it can be expected that a cellulosic nappy, which will be washed countless times, is far more likely to exhibit the effect that any other material.

ash test crucible

Remains of Nappy D after Ash Test – Skeletal residue of the Hydroxyl Apatite clearly showing the form of the cellulosic material it has deposited on. (That material has been consumed by the test itself.)


Side by side – History & Test Results

excel of INOSW results

Snip of Excel worksheet which I have linked below.

Nappy Strip analysis



Interpretation and Analysis

It is probably important to state at this point that this is a relatively small sample (5) and that all of the nappies (bar the control) have exhibited symptoms which have caused them to either loose efficiency as a nappy, or which means that they have become unpleasant or distasteful to use. Given the high cost of testing it is not surprising that this type of test has not been undertaken regularly and in fact I was unable to find any results on-line which mimicked this testing process for reusable nappies/diapers. It would be of the utmost interest to us as members of the cloth nappy community to see further tests undertaken on used but non-symptomatic nappies to see what is “normal” and therefore acceptable and tolerable to the cloth nappy community. As we have only comparison with an unused nappy we are not able to draw any correlations that would indicate how far beyond the “normal use” scale these results fall. We can however call upon the past experience of Ian Strudwick and the team at Shirley Technologies Ltd as to what is normal or expected with these types of used fabrics, although not in the type of use that we subject our nappies to. STL has made some indications within the report as to what they consider to be unusual or outside the normal parameters of their expected results.
STL have indicated that they feel that the solvent tests did not reveal any particularly unusual results and that they would have expected similar results from any like material. I will however direct you to the remark that “only the presence of alkyl benzyl sulphonate on some of the nappies indicates the presence of a detergent residue” which I consider curious as nappies A, D and E all demonstrated some “soaps” and I was also under the impression that “carboxylates” are the main component of compounds such as Calgon which is a water softening agent. I admit to having limited knowledge of how to analyse these results any more closely and will move on from these with a request that any chemists amongst our group look closely at the results and interpret them for the laymen amongst us.


This is a very interesting set of results as it shows a wide variation. The control is showing zero and the most contaminated (G) is showing 34000 colony forming units per millilitre of aliquot which is an incredible number. It is within this set of results that having some comparison to a “normal” used nappy would be useful.
This Bioburden has been shown to generate a “biofilm” on the working surface of the fabric which appears to have a detrimental effect upon the performance of the nappy.

It seems probable that the washing routine is implicated in the loss of performance. Poor washing practice limits the removal of bacteria and these remaining bacteria provide an environment within the fabric which serves to accelerate the multiplication of bacteria at each subsequent use.
Nappy “G” has the highest level of Bioburden, at 34000 cfu/ml (colony forming units per ml of aliquot), and has been washed with an Ecoegg. It has 10 x the level of Bioburden of the other nappies. Considering how badly the Ecoegg fared in the detergent tests and in light of this result I would be very interested in asking Ecoegg to respond to us and send the test results that they promised us last year when we had our live chats. It would appear that even when washing this nappy at 60°C the Ecoegg was not able to remove the bacteria deposited on the working surface and that even repeated washing failed to remove enough bacteria. I hypothesise that this led to the very high level of bacteria deposit on the fabric of the nappy. This nappy is not of the type to be used as a night nappy. It does have a PUL layer. An additional issue with nappy G is that it is labelled as “Wash at 35°C” which according to STL is far below the desired threshold of 74°C which is the NHS standard for sterilising cloth.

Next came the nappies that comprise Viscose from Bamboo– this is a product often touted as having ‘naturally antibacterial properties’ and yet all three nappies A, D and E have significant Bioburden and in fact the nappy with the lowest burden is the 100% polyester nappy B.

The second highest Bioburden nappy is “A” at 5300 cfu/ml. This was washed at 40°C with a half dose of Method liquid. It is a cellulosic type nappy and was used as a night nappy. It does not have a PUL layer.

Next is nappy “E” at 3900 cfu/ml. We have been told it was washed in non-bio but not the dosage. It was also washed at 40°C,. It is a cellulosic type nappy and was used as a night nappy. It does not have a PUL layer.

Then comes “D” at 3400 cfu/ml, which was washed in ½ dose Non-Bio but with the addition of Vanish (dose not given) and at 60°C, it is a cellulosic type nappy and was used as a night nappy. It does not have a PUL layer.

Finally is nappy “B” at 2300 cfu/ml. The washing provenance of this nappy is unknown as I received it pre-loved. I did wash it more than once at 60°C with a full dose of non-bio and a number of rinses but it still smelt faintly of Ammonia and leaked the instant urine touched its working surface.


Ash Tests.
If we take the result for the unused control nappy (0.3%) we can safely state that nappies “G” (0.5%) and “B” (0.6%) did not have significantly high ash levels and this can be attributed to their Polyester composition. As STL explain the Viscose fabric is far more absorbent than the Polyester and as such

“A washed viscose fabric will hydroextract loose water molecules but remain significantly damp to the touch, with the moisture containing the inorganic salts. The inorganic salts then dry and redeposit onto the outside of the fibres to form an “exoskeleton” which is “fixed” as the nappy dries. The same effect is far less prevalent with washed polyester fabric because the fabric will hydroextract almost to dryness and so the inorganic salts are taken to the drain with the water and so are not present to redeposit”

This appears to turn on its head the claim by many manufacturers that bamboo-derived cloth (viscose) has naturally anti-bacterial properties. Disregarding the nappy washed in the Ecoegg, which I speculate has no value as a cleaning product, the cellulosic nappies all performed less well. More testing would be useful to confirm this position.
Nappy A is interesting as it shows an elevated % of inorganic matter (which is what the Ash is) at 3.8% but this cannot be compared to the extremely high levels of nappy “E” at 21.9% and nappy “D” at 20.7%. It would be extremely interesting if we could get some provenance for the water type in the areas where these 3 nappies were washed, perhaps even have the water tested to see what it contains and to see what the level of inorganic compounds such as calcium or any phosphate is in the water. We would then be able to see if there is a correlation between the water type and the level of deposit. (here is Nappy A Water Quality report. These nappies were in a very small rotation being washed every 2 days so approximately 78 times in their 9 months of service). It would be helpful to have this information for each nappy tested and using the document below (provided by Kate Conway) would be helpful for any of us seeking to inform our washing routines. If you contributed one of the test nappies please can you send in your PDF water report and washing frequency? Thank you so much!

Find Your Water Hardness and Quality

It is also pertinent to note that nappy D has been washed at a half dose of non-bio plus Vanish with an extra rinse. According to Cloth Bum mythology this would be considered to be an excellent washing routine as the half dose and extra rinse would avoid any complications from the spectre of “detergent build up”. Yet it is very clear that there is an exoskeleton which was seen under the electron microscope.


This exoskeleton is a “Hydroxyl apatite” and comprises of Calcium and Phosphorus (Phosphates).

There has already been a great deal of discussion around the result of the test on nappy “D” and now that we can see that nappy “E” is similarly affected yet has a different washing history and comes from a different candidate it is even more interesting.

Nappy D is known to have been washed in half dose and it was in active service for 9 months (which is not particularly long, and nappies being expensive items, would normally be expected to last for between 2 to 5 years depending on use). If we were able to establish the size of the rotation i.e. how often it was washed as well as the water type that would inform our findings further.

Nappy E has been in use for 2.5 years so it can be expected that it was washed a large number of times in that period. Again, knowing the frequency of washing and the water type could help us to unravel some of the mystery here.


STL are advocates of the theory that the repeated washing of the items have contributed to the presence of the Hydroxyl Apatite and the Bioburden and they state that

            “Deterioration in performance…over time i.e. with repeated uses and washes is a very real phenomenon. However this is not a problem of “detergent build up” per-se but a combination of soiling not being effectively removed and therefore creating Bioburden, and redeposition of inorganic salts from detergents onto fibre, exacerbated by the presence of hard water. Both effects are created by the fact that nappies are not washed at >60°C.”

I would like to understand more about the science behind this statement, especially regarding the “redeposition of inorganic salts from detergents onto fibre” and how that relates to the dosage. Due to nappy D being washed at half dose it does not seem likely that the effect has come about as a result of a surplus of detergent in the wash cycle. Could it perhaps be that there are Phosphorous compounds present in the piped supply, such as those added to reduce the accumulation of lead from historic pipework in the drinking water supply? Or is there any possibility that the urine and faeces that these nappies contain are adding to the increase in deposition? There are so many questions raised and this is why what we are doing with the NSG is so interesting and compelling.

Web site referencing levels of Phosphate in Urine for adults

A quick google reveals that there is indeed Phosphate present in urine and if there is an issue with the removal of bacteria through insufficent temperature and or detergent within the wash cycle could it also be the case that the urine is not being sufficinetly removed? The residual phosphate in the urine could be working with the calcium from the hard water to lay down these accretions on the fibres of the nappies.


90° Strip Wash

It is worthy of note that STL have indicated the need for temperatures over 74°C to create a sterilising effect and as many/most domestic grade washing machines do not have that temperature option but rather 90°C (and on some higher quality machines an 80°C setting) they opted for this to run their own strip washing experiment. They washed a sample of nappy D at 90°C and found that the Bioburden and the Exoskeleton were removed and that the material regained a much brighter whiteness and the feel of the fabric was much improved.

nappy sample strip wash comparison

While many people will be understandably reluctant to put expensive and beautiful nappies through a 90°C wash I feel that there is certainly scope here for us to inform the manufacturers (of whom we are fortunate to have some in our numbers) that what we need are nappies which can perform well throughout their life, are durable enough to be treated in such a way as to maintain their performance and to ensure that they are sterile enough to a) be used on our own children and b) be transfered through the active pre-loved market to another person’s child. Having washing instruction such as the recommended 35°C on Nappy G means that many people are afraid of sterilising the nappy and that the life of the nappy may actually be shortened by following the label instructions. There is also an argument that Washing Machine manufacturers would be well served to add a 74°C + cycle that is useful for sterilising in a domestic setting (we heard about the disgusting nature of tea towels earlier in the project) but which is not as energy hungry and overheated as a 90°C wash.



 Although we did not find any significant evidence of oils or organic build up within the nappies we did find evidence that there was a Bioburden which had led to a biofilm and also significant exoskeletons formed of Hydroxyl apatie. Both of these phenomena have had a substantial effect on the performance of the nappy.

There does not appear to be a relationship between the formation of  biofilm and the formation of the hydroxyl apatite.

Cellulosic nappies, due to their absorbent nature, are more prone to the formation of an exoskeleton.

Washing at 90°C appears to remove both the Bioburden and the Exoskeleton.

Further work and investigation is required and I look forward to finding out more about the nappies that were tested and seeing if we can have further tests done on “normal” used nappies that are considered to be functioning well.



Topics for Discussion


  • What is the source of the Phosphate which feeds the Hydroxyl Apatite?
  • If all the nappies have Bioburden what is an “acceptable” level of Bioburden?
  • Is the Ecoegg a suitable washing system for nappies?
  • How can we feed back to manufactures about temperature treatments and detergent routines?
  • How can we inform manufacturers around helpful and appropriate labelling?
  • If Cellulosic nappies have more likelihood of Hydroxyl Apatite exoskeleton what further work do we need to do to create appropriate recommendations?
  • Is water hardness indicated in the creation of the exoskeleton?
  • Is under-dosing with detergent leading to Exoskeleton formation?
  • What further work do we need to do to verify these results?
  • Can a chemist explain the Solvent tests in layman’s terms and do they agree with the analysis from STL that there is no detergent build up?
  • Can we get a more complete history of the candidate nappies?
  • If multiple washes are indicated in reduction of performance what advice can we give to improve that performance?
  • Did a PUL layer appear to have any effect on the results?
  • In light of these results can we believe retailers claims that viscose derived from Bamboo has “naturally anti-bacterial properties” and how can we inform their position?
  • Can we get further funding (perhaps from manufacturers) to continue this research?

7 thoughts on “Strip washing results – part 2

  1. Your experiments are really interesting, it’s certainly encouraged me to wash our nappies at 60 more often!

    Could STL put the bioburden results in some sort of context? I’m not familiar with the units cfu/ml so I don’t know what results of 2-5000 really mean. From a quick google search they seem high in the context of medical sterilising but fairly low compared to results from the food industry. So based on this they don’t seem too bad for something which is frequently covered in poo! Could they give any more information or a comparison with other results to show how high the levels really are?


    • Hi Karen! Thank you for your comment! Within the text I explained our desire to do further tests on “normal” nappies, i.e. Ones which have not been identified as being in need of stripwashing, so that we can make comparisons. Our tests are apparently unique so we have nothing to indicate what is acceptable in normal use. If you read the previous blog post about strip washing it has a better explanation of the method for test. In short, a sample of the cloth is placed in a sterile solution and shaken for a minute. That solution is then diluted (in most cases 3 times but for nappy G 4 times) until the colonies in one ml of the liquid are visible and countable in the petri dish. So the cfu (colony forming units) are for every ml of solution after dilution (x 10th the pwr of 3). The lab did say that for fabric they are Huge results but that probably isn’t surprising given the use and poor washing practice. The bacteria create a “raft” or Biofilm on the surface of the fabric and this is implicated in loss of performance, stinks and possibly rash and skin burns


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