The “Hidden Gum” problem: Fomtec examines polymer instability risks in modern SFFF foams
Iain Hoey
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Fomtec explains why “hidden gum” and partially hydrated polymers threaten reliability in modern Synthetic Fluorine Free Foams
Natural polymers – large molecules made of repeating subunits (monomers) that occur in nature – have long been used to build structure and stability in formulated products.
Proteins such as silk or wool, carbohydrates such as starch and cellulose and natural rubber are familiar examples.
Many are biodegradable and in a post-PFAS landscape they are often viewed as a more environmentally responsible route to rebuilding foam blanket performance.
Their use in firefighting foam is also well established.
Natural polymers entered mainstream foam chemistry in the 1970s with the first alcohol-resistant (AR) foams.
Standard hydrocarbon foams such as FP, AFFF and FFFP, when applied to water-miscible fuels like acetone or IPA, struggle to retain a blanket: the fuel disrupts the foam structure and rapidly collapses the bubbles.
The breakthrough was the addition of natural polymers so that, on contact with polar solvents, a polymeric phase would “drop out” and form a barrier between the foam bubbles and the water-miscible fuel.
That polymer mechanism delivered more than alcohol resistance.
It also produced slower-draining foams with stronger bubble structures and improved heat resistance – performance traits that translated into more durable blankets and better burnback security.
As a result, AR-type foams became almost universally adopted from the 1990s onward as the foam agent of choice for large-scale emergency response in high-hazard industries, including scenarios involving hydrocarbon fuel fires where blanket integrity matters most.
The stability problem
From the early 1970s into the 2010s, manufacturers experimented with polymer type and dosage.
The most common natural polymers used were polysaccharides – often simply called “gums” – including Xanthan Gum and Guar Gum.
While specific chemistries differ, the operational trade-offs have remained consistent across the industry:
• Adding polymers increases concentrate viscosity.
• Keeping polymers stable in solution or suspension across the product’s service life is difficult.
Viscosity is often framed as an engineering consideration.
If you know the rheology of a product – and its viscosity response to shear – then pumps, proportioners and pipework can be specified accordingly.
Stability is a different class of challenge.
Every foam manufacturer has encountered stability failures at some point – sometimes driven by batch variation (raw materials out of specification, incorrect dosing), sometimes by storage and climatic conditions in the field.
When stability issues arise, the symptoms are operationally serious: concentrate separation, polymer settling, dehydration effects and in extreme cases near-solidification of the product.
These are operational performance problems that directly affect pumpability, induction accuracy and discharge performance.
Post-PFAS
In fluorine-free SFFF, extinguishing and burnback security now rely primarily on blanket integrity rather than fluorosurfactant film formation, echoing the fundamentals of early protein-based foams.
For many manufacturers, returning to natural polymers has therefore been inevitable.
Natural polymers can materially improve fluorine-free performance by creating slower draining foams, strengthening bubble structure and improving heat resistance.
In general, adding more natural polymer improves fire performance – particularly around sealing against hot surfaces and delivering burnback resistance in saltwater conditions, where polymers can help retain a moist, resilient blanket at the interface.
But the familiar trade-off remains: more polymer usually means more viscosity.
And in today’s installed base, viscosity now directly affects compatibility with existing proportioning and pumping equipment originally designed around different product families.
The market response
That pressure – to achieve strong fire performance without exceeding the viscosity envelope of installed systems – has driven a trend in fluorine-free concentrate design: using partially hydrated polymers to keep “in-can” viscosity attractive while still delivering polymer benefits at the point of application.
At Fomtec, this strategy is described as “hidden gum.”
On paper, this can look like the best of both worlds: good fire test performance paired with manageable viscosity in storage.
In practice, it can embed a latent instability that appears later – after installation, after time in tanks, after exposure to humidity, temperature cycling, shear, or small amounts of water ingress.
The core issue is hydration state. A polymer that remains partially hydrated in the manufactured concentrate can continue hydrating later.
That means the concentrate’s rheology remains capable of changing over time.
In high-consequence emergency response, a product that behaves differently over time becomes a reliability hazard.
The delayed hydration failure mode
Foam systems are inseparable from water.
They connect to water supplies, they live in humid environments and they are handled in ways that can introduce small but meaningful water ingress over years of service.
If a concentrate contains partially hydrated polymers, then water exposure can trigger further hydration, swelling and thickening – sometimes sharply.
Fomtec developed a test protocol to examine viscosity response to water addition, normalising viscosity and then measuring how it changes as water content increases.
When testing three of Fomtec’s own SFFF products, the normalised result behaved as many engineers would expect: viscosity decreased as water was added.
At 15% water addition, the viscosity dropped by roughly 20%.
However, when Fomtec obtained four competitive AR-SFFF products and ran the same protocol, the behaviour was starkly different.
All four competitor products exhibited a normalised increase in viscosity of more than three times with water addition in the range of 15% to 40%.
That difference matters because in the real world, a concentrate that thickens dramatically when contaminated with water can stress or degrade multiple points of a foam delivery chain:
• Reduced pumpability and increased pressure drop
• Proportioner performance drift and induction variability
• Filter/strainer loading and blockage risk
• Nozzle and discharge pattern changes
• System unreliability under emergency demand
Existing viscosity response data provides sufficient basis to identify the hazard: large, unpredictable viscosity increases translate into less predictable flow, proportioning and discharge at the moment systems are expected to work without hesitation.
A metastability problem
The most serious concern with partially hydrated polymers is the potential for unpredictable viscosity increases.
It is that viscosity might increase unpredictably and that the concentrate may be in a metastable state: appearing stable and compliant at manufacture, then transitioning as conditions change.
Metastability in foam concentrates is a reliability problem because it masks risk during early evaluation and acceptance.
A concentrate can meet viscosity specifications at release while still carrying latent thickening capacity that emerges later in storage tanks, pipework dead-legs, or proportioners.
Once that happens, the system can fail in ways that appear mechanical – blocked strainers, inaccurate proportioning, low flow – when the root cause is chemical and structural.
This is why transparent disclosure of polymer strategy is operationally important.
If polymer strategy is explicit, operators can make informed engineering choices about equipment compatibility, storage controls, inspection intervals, or acceptance tests designed to surface instability before an incident occurs.
Fomtec’s stated position is that all polymer-based Enviro SFFFs use 100% fully hydrated natural polymers because the instability linked to variable viscosity from partial hydration is considered too large a risk.
The company also acknowledges that it has not yet established a quantified statistical relationship with blocked pumps or discharge impairment associated with this phenomenon, but argues that a measured viscosity swing exceeding 300% is itself enough to justify caution in high-hazard environments.
On that basis, it calls for manufacturers to declare whether their formulations rely on partially hydrated polymers.
The rush to “1×3”
Alongside chemistry pressures, there is a commercial one: the drive toward simpler portfolios and broader “one product covers more scenarios” positioning – often summarised as a push toward “1×3” solutions.
The concept is attractive: fewer SKUs, less complexity, easier procurement.
But if blanket integrity is now doing the work that PFAS chemistry previously helped with, then a 1×3 ambition raises an awkward formulation question:
How much natural polymer is required to achieve hydrocarbon performance – especially on hot surfaces and for burnback security – and how do you put that quantity into a concentrate without destabilising it?
If higher polymer content is required, manufacturers may use partial hydration to control viscosity.
And that is where the 1×3 rush can inadvertently amplify “hidden gum” risk.
A formulation stretched across a broader operating envelope often sits on tighter balances: more demanding performance targets, more variable water qualities, wider storage conditions and a larger installed base of equipment with differing capability.
Those conditions are exactly where metastability is most likely to surface.
In that sense, a 1×3 approach built on hidden gum may be even more metastable than a 3×3 strategy, because broader coverage can force higher polymer dependency and narrower stability margins while still needing to present a low in-can viscosity for market acceptance.
Performance without the hidden compromise
Fomtec accepts that partially hydrated polymer strategies are attractive when trying to combine performance with manageable viscosity.
The company states it spent more than three years evaluating whether to adopt the approach, but claims that technological breakthroughs within its Enviro Programme enabled a different route: the launch in January 2026 of ENVIRO 3×3 NEO, based on 100% fully hydrated polymers while targeting high performance levels against standards including EN 1568:2018, UL 162, IMO and also LASTFIRE and ICAO Level B.
The implication is significant for the wider market: if top-tier performance can be achieved using fully hydrated polymer strategies, then reliance on partial hydration becomes a clearer formulation choice, particularly in high-hazard hydrocarbon risk where long-term reliability is the primary requirement.
What should change?
The reintroduction of natural polymers into fluorine-free SFFF formulations has delivered real performance benefits.
But the method of incorporation – fully hydrated versus partially hydrated – should now be treated as a safety-critical design choice, not a minor formulation detail.
Partially hydrated polymers may deliver impressive lab and test-house performance and an attractive in-can viscosity while also introducing latent instability that expresses under the most common real-world stressor of all: water.
When water exposure can trigger delayed polymer hydration and viscosity swings of several hundred percent, the concentrate’s behaviour becomes variable after installation – introducing uncertainty into pumpability, induction accuracy and discharge performance.
Foam concentrate evaluation must go beyond controlled extinguishment tests and include long-term reliability questions: how the product stores, how it tolerates water ingress and humidity, how its rheology evolves and how consistently it proportions and discharges across the full range of realistic operating conditions.
As fluorine-free foams become the global norm, transparency around polymer hydration strategy should be viewed as an operational requirement.
In firefighting foams, performance includes long-term behaviour in operational storage and real-world system activation.
It is what happens years later, in the field, when the system is activated and everything depends on the foam flowing exactly as intended.