Isotonic, Hydrogel, and Traditional Gels: Understanding the Main Types of Running Gels
Walk into any running shop and you'll find a wall of energy gels staring back at you. Foil packets in every flavour imaginable, prices ranging from a dollar to nearly five, and brand names that sound more like tech companies than nutrition products. To the uninitiated, they all look roughly the same — small, squeezy, sticky. But underneath that surface similarity, the energy gel market has quietly split into three distinct formats, each engineered around a different philosophy of how to deliver carbohydrates to a working body.
Those three formats are traditional gels, isotonic gels, and hydrogel gels. They differ in carbohydrate concentration, in how they interact with water in your stomach, in texture, in price, and most importantly, in the scenarios where they actually perform best. A gel that works beautifully on a flat, well-stocked road marathon might be the worst possible choice for a hot, self-supported trail half marathon — and vice versa. Choosing the wrong format isn't just a matter of taste; it can mean cramps at mile twenty, a stitch when you need to surge, or a stomach so bloated you'd happily trade your finishing time for a portable toilet.
This guide walks through what separates the three main types of running gels, why each one exists, and how to figure out which format genuinely suits the runner you are. By the end, you should be able to read a gel packet, understand what it's promising, and pick the right tool for the run in front of you — rather than buying whatever happened to be on the shelf near the till.
What Actually Defines a "Type" of Running Gel
Before you can compare gels meaningfully, it helps to understand what the industry is actually sorting them by. The categories aren't marketing inventions — they reflect real differences in how a gel is formulated and, more importantly, how it behaves once it hits your stomach mid-run. The three properties doing most of the heavy lifting here are carbohydrate concentration, osmolality, and the delivery mechanism that ties them together.
Osmolality: The Hidden Property That Decides Everything
Osmolality is a word you'll almost never see on a gel packet, but it dictates whether a gel sits comfortably in your gut or causes the kind of distress that sends runners ducking behind hedges. Put simply, osmolality measures how concentrated a fluid is — specifically, how many dissolved particles it contains per kilogramme of water.
Your body fluids sit at roughly 280 to 300 mOsm/kg. When you swallow something more concentrated than that, your gut pulls water in from surrounding tissue to dilute it before absorption can happen. Drag enough water into the intestine and you get the classic gel-related complaints: sloshing, bloating, cramps, and the dreaded urgent dash off-course. A traditional gel can run anywhere from 1,500 to 3,000 mOsm/kg — five to ten times more concentrated than your blood. That's precisely why it needs a chase of water to dilute it before it can be processed.
This single property is the lens through which the three main formats split apart. Traditional gels accept high osmolality because it lets them pack maximum carbs into a tiny packet. Isotonic gels deliberately lower their osmolality to match your body, accepting a larger packet in exchange. Hydrogels sidestep the osmolality problem entirely by changing where digestion happens. Understanding this trade-off is the key that unlocks every other comparison in this article.
Carbohydrate Concentration and the 20–40g Spectrum
The second variable is how much carbohydrate each packet contains. The industry standard sits around 20 to 25 grammes per gel, which has held steady for years because it maps neatly onto guidance around 30 to 60 grammes of carbs per hour — roughly two gels.
But the spread has widened considerably. You'll now find gels with as little as 20 grammes of carbs (typical Maurten Gel 100, GU Original) and others packing 40 grammes (Maurten Gel 160) or even 30 grammes in a smaller, denser format (SiS Beta Fuel). Brands manipulate this number deliberately. A bigger carb load per packet means you can carry fewer sachets, but it also forces the formulation in particular directions — usually thicker, sometimes sweeter, occasionally needing a specific glucose-to-fructose ratio to stay absorbable.
The takeaway is that carb concentration isn't just a number on the back of the packet. It signals what the gel is trying to be. A 20-gramme gel is a sip; a 40-gramme gel is a meal. The format type often follows directly from this choice.
Why Texture Tells You More Than You'd Think
The final defining property is texture, and it's tempting to write this off as personal preference. It isn't. Texture is a functional signal of formulation. A thick, syrupy gel is concentrated and almost certainly high in osmolality. A thinner, more watery gel has been diluted on purpose, usually to make it isotonic. A jelly-like gel that holds its shape and slides out of the packet as a single blob is almost always a hydrogel — that texture is the encapsulation matrix doing its job.
When you compare energy gels for runners across categories, you'll notice these textural cues line up almost perfectly with formulation type. Once you know what to look for, you can often classify a gel just by squeezing a tester onto a spoon at the shop counter. Thick and sticky points to traditional. Runny and almost drink-like points to isotonic. Wobbly and tofu-adjacent points to hydrogel. The packet might dress the product up in fancy branding, but the texture rarely lies about what's inside.
Traditional Gels: The Original Format That Still Sets the Standard
Traditional gels are where the entire category started, and despite the newer formats getting most of the buzz, they remain the best-selling and most widely available option in any running shop. GU Original, SiS Go Energy, PowerBar PowerGel, Clif Shot — these are the names that built the sports nutrition aisle. Understanding how they work isn't just historical interest; it's the baseline that makes every other format make sense.
The Maltodextrin and Fructose Backbone
Almost every traditional gel is built on the same fundamental recipe: a blend of maltodextrin and fructose. Maltodextrin is a complex carbohydrate made up of short chains of glucose, derived usually from corn, rice, or wheat starch. It tastes only mildly sweet, dissolves cleanly, and gives the gel its bulk. Fructose is added in smaller amounts to bring sweetness and, more importantly, to unlock a separate absorption pathway in the gut.
The reason this combination became the industry standard comes down to absorption ceilings. Glucose-based carbs (including maltodextrin, which breaks down into glucose) are absorbed through one specific transporter in the intestinal wall called SGLT1. That transporter caps out at about 60 grammes of glucose per hour. Fructose, on the other hand, uses a different transporter — GLUT5 — which adds another 30 grammes or so of absorption capacity on top. Combine the two in a roughly 2:1 ratio of glucose to fructose, and suddenly your gut can process up to 90 grammes of carbs per hour rather than 60 — a physiological advantage that becomes even more significant when digestion is already compromised by race-pace effort. That's the entire reason traditional gels are formulated the way they are, and it's the foundation every newer format has built upon rather than replaced.
The Syrupy Consistency Has a Purpose
Pick up a packet of GU or PowerBar PowerGel and you'll notice it feels weighty for its size. Tear it open and the contents move slowly, like warm honey. That viscosity isn't laziness on the manufacturer's part — it's the mechanical consequence of cramming 20 to 25 grammes of carbohydrate into roughly 32 grammes of total product. There simply isn't much water in the packet.
This concentrated approach is what makes traditional gels so portable. A few sachets weigh almost nothing, slide easily into a running belt or shorts pocket, and don't take up the volume a comparable amount of fluid-based fuel would. For a runner doing a flat half marathon with aid stations every couple of miles, that compactness is genuinely useful. The trade-off, of course, is that the thickness comes with consequences for digestion — which brings us to the rule that defines this entire category.
The Water Chaser Rule and Why It Isn't Optional
Here's the hard rule with traditional gels: you need water with them. Not as a polite suggestion, but as a physiological requirement. Remember the osmolality discussion from the previous section? A traditional gel sits at three to five times the concentration of your bodily fluids. Swallow it without water and your gut has no choice but to pull fluid in from the surrounding tissue to dilute it before absorption can begin.
That's where most gel horror stories come from. Runners take a gel at an aid station, grab a few sips of water, and feel fine. Runners take a gel two miles before the next aid station, run hot, and end up with a stomach that feels like a churning washing machine. The general guideline is at least 150 to 200 millilitres of water within a few minutes of taking the gel — roughly a small cup at a marathon aid station. Skip the water and you're not really benefiting from the carbs anyway; they're just sitting in your gut waiting to be processed.
This water dependency is the single biggest practical limitation of the traditional format. It works brilliantly on a well-stocked road race, on a treadmill, or on a planned loop past a water fountain. It works far less brilliantly on a self-supported trail run in summer, where carrying enough water for every gel becomes its own logistical headache — and the same constraint applies to any endurance sport where bonking mid-ride leaves you with depleted bottles and no room to chase a gel. That gap in the market is precisely what gave the next two formats their reason to exist.
Isotonic Gels: The Pre-Hydrated Answer to the Water Problem
If traditional gels demand water, isotonic gels arrive with the water already built in. The format was popularised by Science in Sport (SiS) with their Go Isotonic Energy gel, and it has since spawned a small but meaningful corner of the market that solves one very specific problem: what do you do when you need carbs but you can't reliably get water?
What "Isotonic" Actually Means in Practice
The word gets thrown around in sports marketing so often that its meaning has blurred. In physiological terms, isotonic describes a fluid that matches the osmolality of human bodily fluids — that 280 to 300 mOsm/kg range we covered earlier. When you swallow an isotonic fluid, your gut doesn't need to pull water in to dilute it. The fluid passes through the stomach quickly and gets absorbed in the small intestine without the gut-water shuffle that traditional gels trigger.
For a gel to genuinely be isotonic, the manufacturer has to dilute the carbohydrate solution significantly. That's why an isotonic gel packet is noticeably larger and heavier than a traditional one — often 60 grammes of total product versus the 32 grammes of a standard gel. The carbs are the same or slightly less; the water content is dramatically higher. You're essentially carrying a pre-mixed sports drink in gel form rather than a concentrated syrup.
The practical upshot is straightforward. Tear open an isotonic gel and you can swallow it without a sip of water afterwards. Your stomach won't punish you for it. That single property changes which races and training scenarios the format suits.
The Trade-Off You're Signing Up For
There's no free lunch in gel formulation, and isotonic gels pay for their water independence with two real downsides. The first is sheer bulk. Carrying six isotonic gels for a marathon means carrying roughly 360 grammes of product, compared to about 190 grammes for the same carb load in traditional format. That's a noticeable difference when it's bouncing around in a race belt for three or four hours.
The second is carb density per gramme. Because isotonic gels are diluted, you get less fuel per millilitre of product. A standard SiS Go Isotonic gel delivers 22 grammes of carbs in 60 grammes of product, which is roughly the same carb hit as a traditional gel but with double the packaging mass to manage. For runners chasing the upper end of carb intake — 70 to 90 grammes per hour — that means carrying more sachets or supplementing with another fuel source.
There's also a flavour consequence worth flagging. Because the formulation is more dilute, isotonic gels tend to taste milder, sometimes almost watery. Some runners find this far more palatable than the sweet, syrupy hit of a traditional gel. Others find it underwhelming. As with everything in this category, it comes down to testing during training rather than discovering your preferences on race day.
Where Isotonic Gels Genuinely Outperform
The scenarios where isotonic gels shine all share a common feature: limited or unreliable access to water. Hot-weather running is the obvious one. When you're already drinking your water supply just to stay hydrated, having to dedicate sips to chasing a traditional gel feels like rationing. An isotonic gel lets you spend your water budget on hydration rather than digestion.
Trail and ultra-distance running is the second strong use case. Self-supported events where aid stations are an hour apart, or unsupported long runs where you're carrying everything in a vest, make the water-chaser rule of traditional gels genuinely awkward. An isotonic gel lets you fuel on a climb or a technical descent without breaking stride to fumble for a flask.
The third scenario is more subtle: runners with sensitive stomachs who struggle with the concentrated punch of traditional gels but don't want to spend hydrogel money. Isotonic formats sit at a moderate price point — generally only slightly more expensive than traditional gels — and the lower osmolality often takes the edge off GI distress without requiring a complete reformulation. For runners building up their gut tolerance, isotonic gels can be a useful middle step rather than a permanent home.
The isotonic format hasn't replaced traditional gels and it wasn't designed to. It carved out a specific niche where the water problem genuinely matters, and within that niche, nothing else does the job as cleanly.
Hydrogel Technology: How Maurten Rewrote the Rules
In 2015, a small Swedish company called Maurten launched a product that didn't fit either of the existing categories. It wasn't a thinner, dilute isotonic gel. It wasn't a thicker, syrupy traditional gel. It was something that wobbled on a spoon like a piece of jelly, tasted of almost nothing, and cost roughly twice as much as anything else on the shelf. Within a few years, it was being squeezed down the throats of Eliud Kipchoge during his sub-two-hour marathon attempt, sponsoring the Boston, Berlin, and Chicago Marathons, and forcing every other gel brand to either copy the technology or explain why they hadn't.
That product was the world's first hydrogel sports gel, and it represented the first genuinely new approach to fuelling in decades.
The Encapsulation Mechanism That Makes It Different
Hydrogel technology doesn't change what's being delivered — it changes where digestion happens. The carbohydrates inside a Maurten gel are still the familiar glucose-and-fructose blend, mixed in the now-standard ratio that maximises absorption. What's different is that those carbs are encapsulated inside a matrix made from two natural ingredients: alginate (derived from seaweed) and pectin (the same stuff that sets jam).
In the acidic environment of your stomach — pH around 2 — the alginate and calcium ions cross-link to form a stable gel. Your stomach essentially can't break it apart. The hydrogel passes through largely intact, dragging the carbohydrate cargo with it. Once it reaches the more neutral pH of the small intestine, the matrix breaks down and the carbs are released directly where they're absorbed.
The functional consequence is significant. Because the gel doesn't actually dissolve in your stomach, your gut doesn't have to deal with a concentrated hit of carbohydrate sitting there waiting to be processed. There's no osmotic pull on surrounding tissue. No sloshing. No bloating. The gel behaves as if it's barely there until it reaches the place where it can actually do its job. For runners who've spent years trying to find a gel that doesn't trigger GI distress at race pace, that mechanism feels close to magic.
The Texture and Taste Are Functional, Not Cosmetic
The first time you open a Maurten gel, the experience is genuinely strange. The contents don't squeeze out — they slide out as a single wobbling lump. It's almost flavourless, slightly sweet at most, with no acid bite, no artificial fruit punch, no glycerin sting. Some runners love it immediately. Others find the neutrality unsettling, like eating a cube of unset jelly mid-stride.
Both reactions are missing the point slightly. The texture and the blank flavour aren't aesthetic choices — they're direct outcomes of the formulation. Adding flavouring agents, acids, or preservatives would interfere with the alginate-pectin matrix, so Maurten leaves them out. The wobbling lump is what an intact hydrogel looks like before it reaches your intestine. If it slid out like syrup, the technology wouldn't be working.
This is worth understanding because it explains why the imitator products that have followed — and there are now several, including PrecisionFuel's range, Neversecond, and some SiS Beta Fuel variants — share many of the same sensory traits. If a gel claims hydrogel technology but tastes intensely sweet and pours like a traditional gel, something has been compromised. The wobble is the whole point.
Why the Premium Price, and Who It's Actually For
Hydrogel gels typically retail for around $3.50 to $4.50 per sachet, compared to $1.50 to $2.50 for traditional and isotonic options. Across a marathon training cycle, that gap adds up to real money — easily a few hundred dollars more across sixteen weeks of long runs and the race itself.
The honest answer to "is it worth it" depends entirely on who's asking. For runners chasing a marathon time goal, where a single bout of mid-race GI distress can cost five or ten minutes and potentially derail the entire race, the premium is often worth paying — at least for the race itself. For runners with genuinely sensitive stomachs who've struggled with both traditional and isotonic formats, hydrogel may be the difference between fuelling successfully and not fuelling at all. For elite or sub-elite athletes pushing the upper limits of carb intake at 90+ grammes per hour, the gentler gut response makes high-volume fuelling more achievable.
Where hydrogel is less obviously worth the premium is in routine training. Slogging through a relaxed long run on a Sunday morning doesn't demand the gentlest possible fuel — your gut is rarely under the same stress as it would be at race pace. Many serious runners adopt a split strategy: cheaper traditional or isotonic gels for training, hydrogel reserved for race day and the longest, hardest training sessions where stomach reliability matters most.
The wider category of energy gels for runners has been measurably reshaped by hydrogel's arrival. Every major brand now offers some version of an "easy on the stomach" gel, even if not all of them use true hydrogel encapsulation. That shift in expectations — that a gel shouldn't make you feel worse than it makes you feel better — is the lasting legacy of the format, regardless of which packet you eventually choose.
