Sewing doesn’t usually involve much fire & scientific observation, but today on the blog we’re putting on our lab coats and goggles for some fun experiments that will include both!
If you’ve been reading the blog for a while, you’ll know that I’m a bit of a fabric hoarder… and while I have *tried* to be strict with my fabric buying over the last few years, I haven’t yet gathered the strength to turn down the big wonderful mystery bags of fabric that my relatives (and friends of relatives…and relatives of the friends of my relatives) send my way after cleaning out their cupboards. So due to my almost-non-existent will power (and the not-so-good memories of my loved ones), I have a lot of fabric in my stash with unknown origins and mysterious compositions!
Knowing the fibre content of your fabric can be really important sometimes, like when you’re making pot-mits and need to know whether a fabric is likely to melt, or when you need to know how best to wash an awesome piece of fabric without ruining it. Other times, knowing the composition of your fabric can just be for your own curiosity and because you want to do fun experiments!
Either way, today we are going to be observing the way fabrics react when burnt, as well as paying attention to some of their other characteristics, to determine what they might be composed of. We’re looking at 3 main groups of fabric – cellulose, synthetic and protein – and the most common fabrics from those categories that you’re likely to encounter, all which are going to have their own reactions and characteristics. When doing a burn test, we can look at how the fabric reacts to the flame, how it ignites and burns, what it smells like, what colour smoke and flame it has and what is left over once it has been burnt. By looking at all of these indicators and comparing them to the way that our common fibres are known to react, we can hopefully identify the compositions of our mystery fabrics!
We’ve even created a handy burn test booklet (that you can access in our Resource Library by signing up to our newsletter here) to guide you through this process which also includes a super useful notes page for you to gather your observations in!
Let’s get started!
Safety, Prep & Method
Before we jump in though, lets just run through a few important safety things:
- We’re going to be setting things on fire, so clear your space of anything flammable! Set yourself up over a bowl or baking tray that can keep your tests confined and have something on hand to help extinguish a flame in case anything does go awry, like a water source or fire blanket. Doing tests directly over the sink can work great, as it’s contained, has easy access to water and it’s also super easy to clean up after!
- Another important safety consideration is ventilation. Make sure you’re set up in a place which has adequate airflow (but not windy – let’s not have something on fire being blown about the house), especially when working with fabrics you suspect to be synthetic, as they can have toxic fumes that you don’t want to be breathing in directly. Even non-toxic smoke isn’t good for you though, so just be mindful!
- To hold your swatch while you burn it, you will need a pair of metal tweezers or if you want even more distance between your hand and the hot thing, then you can also use a pair of metal tongs. For your point of ignition, you can obviously use a lighter or a match, but I like to have both of my hands free, so lighting a candle that can stay stationary while I work is my go-to.
- And lastly – for the actual fabric you’re going to be testing. Ideally your swatches should be a little square 1-2″ in size – big enough to see what’s happening and have time to observe the reaction, but small enough that they’re not creating too big of a flame that we could lose control of!
To test our swatches, we are going to take them one by one with our tweezers and bring them slowly into contact with our ignition source. It’s important to do this slowly as even the way the fabric responds to being near heat, can be an indicator. Once the swatch has been ignited and has burned long enough for you to have observed its reaction, you can blow out the flame, make sure it is fully extinguished, record your findings and move on to the next swatch.
So, now we are set up, have thought about safety and know what we are doing – let’s dig into the possible candidates for our mystery fabric!
The first group of fabrics we’re going to look at are the ones made with cellulose fibres – basically anything that comes from plants. Natural cellulose fibres are bio-degradable and tend to be breathable & absorbent. In terms of their reactions to burn tests, plant based fibres will ignite quickly, burn instead of melt, smell like burning paper and will result in a small amount of soft ash, that powders into nothing when touched.
Linen (aka our favourite) is made from the fibres of the flax plant and is known for its breathability and its tendency to crease easily, which is because of the fibre’s low elasticity. It’s a strong fibre, that softens over time and is commonly used in textured, looser weave fabrics, which means linen is drapier then some other cellulose fibres like cotton.
When it comes to being burnt, linen:
- Doesn’t shy away when it encounters a flame
- It scorches first, then ignites and burns quickly, even when removed from the ignition source
- As it burns you’ll notice a yellow flame and white or grey smoke
- When the flame is extinguished, it does have a small amount of afterglow
- Like all cellulose fibres, it produces an odour of burning paper or wood
side note: let’s talk about blends…
When it comes to mixed composition fabrics, determining their content can be difficult and often impossible. This is especially the case when the fabric is made up of multiple fibres of the same category (cellulose, synthetic or protein) as the reaction tends to be indistinguishable from an unblended fabric. It’s when the categories of fibres are mixed however, that our burn tests can still be useful, and we can get at least a hint of what the fabric is composed of.
The swatch below was from a roll of deadstock fabric that was labelled a linen cotton blend. Linen and cotton have very similar burning properties, so we’d expect that it would scorch, burn quickly with white or grey smoke and deteriorate into ashy residue. However, it reacted slightly differently!
- It pulled away from the flame, burnt with a black smoke
- its residue was crisp with a slight hint of plasticy-ness to it.
- When it was extinguished, the edge was also pulled in & tight which left the swatch puckered.
This tells us that this fabric might actually have a small amount of synthetic content in its composition! We might not exactly what that fibre is, but we know it’s there and that’s pretty handy.
Ahh cotton – a fibre you’d probably be able to find in just about every household across the world. It’s popular for its strength, breathability, relative affordability and its versatility – being found in the form of the heaviest denim & canvas, all the way to the softest floaty voile. It’s generally softer & smoother than linen, and while it has a slightly higher elasticity than the flax fibre, it is also a fabric known for its tendency to crease.
In terms of its reactions to the burn test, cotton burns very similarly to linen, but with a couple of small differences:
- Cotton doesn’t shy away from the flame, it burns with a yellow flame, smells of burning paper or wood and produces white or grey smoke
- It first scorches, like linen, but will sometimes flare when it ignites before burning quickly and continuously when removed from the ignition source
- When the flame is extinguished, cotton has a strong afterglow that is more substantial than other cellulose fibres
- Cotton will produce a light and feathery ash, unless it is mercerised, in which case it create a black ash (Mercerisation is a treatment applied to cellulose fabrics to increase their lustre, encourage dye-ability, increase its strength and reduce its shrinkage)
Processed Cellulose Fibres
Processed cellulose fibres are a strange bunch that somehow don’t completely belong in either the cellulose or synthetic families. They are man-made natural fabrics, which means that they are produced via a chemical synthesising process – like synthetic fibres – but instead of using derivatives of oil, coal & natural gas to create the fibres, they use sources of regenerated cellulose like wood pulp. Like cellulose fibres they are breathable and generally easily to crease, but they have great drape thats more akin to synthetic fibres.
When burnt, because their molecular structure is still the same as other cellulose fibres, despite their production method, they react very similarly to the fibres we’ve covered so far:
- They will burn instead of melt, have light coloured smoke and yellow flames, smell like burning paper and have a grey, ashy residue that breaks down to nothing
- In general, rayon has less of an afterglow compared to cotton, but there is still some burning present after the flame is extinguished (seen in the bottom right photo)
- Rayon & other processed cellulose fabrics also sometimes curl slightly as they burn
Aside from our burn test reactions, another characteristic of processed cellulose fibres that can be used to distinguish it from other cellulose fibres is how its texture changes when wet! The typically soft & drapey fabrics can suddenly feel canvasy, rough and stiff.
Our second fibre group includes fabrics that are man-made – being produced by joining chemical monomers into polymers using a chemical reaction called polymerisation. Synthetic fibres are generally very crease resistant, have low absorbency and breathability but are quick to dry and depending on the weave of the fabric, quite well draping. Because they are created from derivatives of oil, coal & natural gas., when it comes to their reaction to burn tests they will generally melt instead of burn, will release black & hazardous smoke and will be left with a hard plasticy residue that is difficult or impossible to crush. There is a bit more variety between their reactions compared to cellulose fibres though, so let’s dig into the specifics!
Polyester is possibly the most common of synthetic fibres used in clothing and comes in a huge variety of forms. It’s created by pushing molten polyethylene terephthalate (PET) through a spinneret to form fibres that are then chemically treated and woven together. It’s highly durable (which also means it’s not biodegrabable), has excellent resistance against wrinkling and its low absorbency helps it deflect moisture which means it is very resistant against stains & dries quickly. This also means however, that it has low breathability and can make clothing very hot to wear!
When burnt, polyester:
- Shrinks away from the flame before making contact with it
- Either igniting briefly & melting, or simply melting without a flame at all, curling back as it melts
- If the ignition source is held to the fabric long enough for it to catch fire, its flame is bright and orange but also spluttery and will progress slowly through the fabric
- Produces heavy black smoke and hazardous fumes that have a sweet chemical odour
- Creates round, hard black shiny plastic beads along the edge of the fabric that can’t be crushed when cool, but when still hot can drip from the fabric
It’s incredibly commonly to find polyester blended with more breathable and comfortable fibres a frequently occurring blend being poly-cotton. We saw the reaction of a linen/cotton blend earlier, but let’s look at a fabric with an even higher percentage of synthetic content:
- Our poly-cotton swatch was quick to flare dramatically like cotton, and to continue burning when removed from the ignition source
- Instead of just burning though, the edge was bubbling with the appearance of a liquid and was curling away as it melted.
- Despite its fast ignition and dramatic orange flame, its progression was relatively slow through the fabric and the flame was slightly spluttering.
- It produced black smoke which had a chemical smell
- When extinguished, it was left with a crispy, rough edge that was curled back. The looser sections of the edge were relatively easily crushed into gritty black residue, but a harder less crushable boarder was left along the unmelted fabric.
Nylon, while not as widely used as polyester because of its price, is another common fibre found in a lot of activewear fabrics and non-fabric applications such as ropes, tents and carpet. This is because nylon is very strong, more so than polyester and has great elasticity! It is washed and dyed easily, is abrasion resistant and its filament yarns mean that the fabric it creates is smooth, soft & lightweight.
When burnt, nylon will:
- Shrink away from the flame before igniting & melting quickly
- Have a spluttering flame that is blue at its base and orange at its tip
- Drip like tar as it melts, releasing a black & hazardous smoke with fumes that smells strongly of celery gone bad
- Will sometimes self-extinguish unless contact with ignition source is maintained
- Once extinguished, will be left with round, hard grey plasticy beads along the melted edge of the fabric that wont crush once they have cooled.
Acetate is a bit of a funny one in the synthetic group and is a lot like rayon in that it combines a man-made synthesising process with cellulose components. In general though, the fibre’s properties are closer to those of other synthetics. Acetate is often used as linings as it can be soft, cool and smooth, with silk-like sheen & aesthetics. It has good drape and washes well, but has relatively low breathability as well as low elasticity and wrinkle resistance (the later being similar to cellulose fibres).
When burnt, acetate:
- Fuses away from the flame, blazing and igniting quickly
- Splutters & melts, dripping like tar
- Produces a black smoke with hazardous fumes that smell of hot vinegar
- Results in hard black ash or irregular shaped, shiny black beads along the edge of the melted fabric that are difficult to crush.
A final indicator of acetate is that a small scrap of it will actually dissolve when placed in an acetone nail polish remover!
Acrylic is another really common synthetic fibre that is used a lot in knit wear. This is because it is manufactured mostly as a filament, cut into short staple length fibers similar to wool hairs and then spun into yarns. This airier and more textured structure means that it is lightweight and soft and can contain heat between its fibres to create a warm, fluffy and wool-like feel, compared to the smooth & swishy simple filament structures of other synthetics. It can’t mimic the absorbency of wool though, so while it is warm, it is not very breathable! But it is very machine-washable, fast drying, hypoallergenic, and extremely colorfast.
Acrylic is also more flammable than most other synthetics and when burnt will:
- Shrink away from the flame but ignite quickly, flaring
- Melts with a spluttering flame and black smoke
- Hazardous fumes have an acrid and fishy odour
- Left with hard, irregular shaped black plasticy beads that won’t crush
The final synthetic fibre that we’re looking at today is spandex , also known as Lycra, elastane or polyurethane. This fibre has a rubber-like quality which gives spandex its excellent elasticity as well as very high abrasion and wrinkle resiliency. It is also very durable, even more so than rubber itself – and can be stretched more than 500% without breaking! It is almost always combined with other fibres however because of its cost and because even a small percentage of spandex can increase a fabric’s elasticity by a significant amount, so a pure spandex fabric is relatively unnecessary. Spandex is relatively flammable, so when combined with other fibres, it will also accelerate their combustion, but when burnt as an individual fibre it:
- Fuses & shrinks away from the flame
- Melts & burns quickly
- Produces hazardous fumes that smell sharp and bitter
- Results in a soft, sticky & gummy black ash
Last but not least, our third group are the protein fibres, which are natural fibres derived from animals instead of plants. Protein fibres have such distinctive reactions and characteristics which makes them some of the easiest to identify the presence of, which is awesome because they are also the fibres which need the most special treatment in terms of washing & storage, so knowing your fabric is made up of these fibres is important!
Protein fibres are breathable, biodegradable, highly absorbent and have good elasticity, meaning they can hold their shape better and don’t crease as easily as cellulose fibres. Another interesting characteristic of protein fibres is that they have relatively low flammability – especially wool!
Silk is such a cool fabric! It’s created from proteins that certain types of insect larvae (but in terms of the world’s silk production, specifically the mulberry silk worm) secrete to make their cocoons and is the only continuous filament natural fibre! Silk is incredibly strong, partly due to the length of its fibres, which are usually unravelled as a single length from the cocoon, but are sometimes extracted as shorter lengths when the silkworm is allowed to break free of its cocoon.
Silk gets its beautiful lustre from the triangular prism-like structure of its fibres which refract the light to produce a beautiful optical effect. Like most natural fibres it is breathable, but is even better at thermal regulation than cellulose fabrics. It has decent elasticity, so is flexible and quite wrinkle resistant and is also fairly absorbent, although water does weaken the fibres so care must be taken while washing. One quite good indicator of silk is actually its smell when wet, which is quite distinct, especially in its rawer, less processed forms.
Now we get to the interesting part however, its reaction to burn tests!
- Silk is hesitant to burn, smouldering and curling away from the flame initially, and only catching fire when its contact with the ignition source is maintained
- It splutters and sizzles as it burns slowly, producing a light grey smoke and a very potent odour of burning hair
- As it smoulders it produces large round bubbly beads that are hollow, textured and dark grey in colour, with a slightly similar sheen and appearance to graphite.
- The beads are brittle and crisp – easily crushed into a gritty ash
Before moving onto our next fibre, lets quickly have a look at a silk cotton blend, which is one of the most common pairings with silk. This combination of fibres is usually produced as fine, light weight fabrics like voile that thanks to the silk, tend to have even better drape than their pure cottons counterparts. They also often have a slight sheen to them and are smoother and less scrunchable. As for their burn test characteristics:
- Because of the cotton content, silk cotton blends will be faster to ignite and will burn more readily, as seen in the swatch below which is 70% cotton.
- It doesn’t bubble in the same way that pure silk does, but can have a slight sizzle. It has an afterglow once the flame has been extinguished and it’s residue is ashier than that of silk, but less than cotton – often first breaking up into stringy fibres that stay in tact longer before becoming powdery.
- And finally, the most distinguishing characteristic that alludes to the silk content is the smell of burning hair that is still present.
Another super interesting fibre and our last of the day is wool! It can come from a variety of animals, but is most commonly sourced from sheep. It’s breathable, an amazing temperature regulator, is absorbent & moisture wicking, has good elasticity and wrinkle resistance and is durable to top it off. Like silk, one very obvious distinguishing feature of wool is its strong smell while wet. The potent “wet animal smell” is hard to miss, so wetting a small sample of your fabric with cold water is probably easiest and fastest way of being able to tell if it is wool. It is, however, also quite distinctive when being burnt:
- Wool ignites slowly and is very hesitant to burn, even more so than silk
- Once lit, wool will smoulder and curl away from the flame, distinctly sizzling as it slowly burns
- Its flame flickers and appears to struggle, and will often extinguish itself when it’s removed from the ignition source
- Its smoke is a light grey and it has a potent odour of burning hair or feathers
- Hollow, black & irregular textured and shaped beads form on the burnt fabric edge that tend to look tight and drawn in. It is darker in colour and more sinewy in appearance than grey bubbly silk beads.
- Its residue has a slight sheen and is easily crushed into gritty ash, but is slightly harder than that of silk.
Wool is also another popular fibre to blend with and we can see below that in our last swatch of the day – a wool/cotton blend, how it reacts distinctively with the properties of both fibres. The cotton makes it fast to ignite and burn with a yellow flame and grey smoke. The sizzle, smell and hollow gritty residue on the other hand make it obvious there is wool present. So definitely a delicate wool wash detergent for this one!
And that’s it folks, now we know all about the fibres we’re likely to encounter, we’re ready to start testing and investigating our own mystery fabrics! We’ve covered so much today though, (way too much to remember while burning something and observing reactions and making sure you don’t set anything else on fire) so here is a handy chart to keep by your side as you’re testing, that summarises everything you need to know.
So get out there and start testing – remembering to be safe while you do it and document as you go. Good luck and let us know how you go in the comments section below!
All experiments and activities involving naked flames have the potential for safety issues.
All activities and experiments presented in this blog post and booklet should be used or tried with caution and good common sense judgment.
Megan Nielsen Patterns shall not be held responsible for any damages or injury resulting from any activities contained in this blogpost or accompanying booklet.
You safety is your own responsibility.