Your choice of stemming plug is specific to your operation’s needs. On some blasts, your biggest win comes from tightening collar confinement and cutting flyrock without increasing cost per hole. For others, the real problem lies deeper in the column. That could be water, cavities, or the need for deliberate air decks to manage powder factor and vibration.
We compare Varistem stemming plugs to Gas Bag® self-inflating borehole plugs to show where each one fits best. We evaluate cost, diameter coverage, explosive compatibility, mechanisms, and real-world performance, then outline when Varistem is appropriate and when Gas Bags offer a better option.
Varistem plug pricing scales with hole diameter, starting at around $1 and reaching about $16.13 per plug. It allows you to size each plug to the actual hole diameter and keep the cost per hole under tighter control, even across mixed blast patterns and varying rock conditions.
Gas Bag units sit in a mid- to upper-cost bracket for stemming and decking. They’re sold in cartons of 10-30 bags, with per-bag prices typically US$8-15, increasing with hole diameter. That means each of the Gas Bag’s pricing is a noticeable jump in cost per hole compared to basic stemming plugs.
Varistem is a low-cost stemming plug with a clear diameter-based price ladder. Gas Bag® units, by contrast, generally fall in the US$8-15 per-bag range and are sold in smaller carton counts. Varistem is an everyday stemming plug for large mines, while Gas Bags can be reserved for specific blasts that justify the higher per-hole spend.
Varistem plugs cover blasthole diameters from 1.75″ to 10″ (about 45 to 251 mm). Each size is engineered for a specific diameter range, so you can match the plug closely to the drilled hole.
Gas Bags self-inflating borehole plugs are available for blastholes from about 3″ up to at least 16″ in diameter (roughly 76-406 mm). Larger special-order sizes are listed in the Stemlock catalogue. Each unit is sold for a nominal hole size (for example, 3″, 4″, 6″, 8″, 10″, and 12″) and is designed to cover a specific-diameter window.
Varistem provides size-specific coverage from 1.75″ to 10″ (≈45-251 mm), making it well-suited to small- and medium-diameter production holes. Gas Bags pick up from around 3″ and run to at least 16″ (approximately 76-406 mm), with larger options available. Gas bags are better suited to larger drill holes.
Varistem plugs work with most standard commercial explosives. Engineers can use Varistem for air decking, helping reduce explosive consumption per blast.
Gas Bag units are non-explosive devices. Engineers can use them with most common commercial explosives, including ANFO, emulsions, water gels and heavy ANFO blends.
Both products are compatible with standard commercial explosives. Explosive compatibility as a metric is therefore not a reason to choose one over the other; other factors will be.
Varistem uses a tear-resistant dip-moulded body. As the blast fires, the initial shock wave drives the stemming material up into the plug and creates a temporary high-pressure seal in the hole. The benefit of this is that it improves early confinement, sharpening fragmentation and making more efficient use of the rock’s explosive energy.
Gas Bag units use a self-inflating, chemically activated bladder placed at depth in the blasthole, which is triggered to expand. As the internal gas forms, the bag inflates tightly against the borehole walls and locks in position, either supporting stemming above it or creating an air deck between explosive columns. Gas bags give you options for cheaper explosives in wet holes and better control in problem holes.
Varistem improves blasting by sealing at the collar. Gas Bags work deeper in the hole to support stemming or create an air deck between charge segments. That makes the Gas Bag a great tool for water sealing and deliberate air decking, while Varistem is a low-cost choice for everyday collar confinement and fragmentation control.
Independent field trials back up Varistem’s results. In one underground platinum mine, Varistem delivered a steady 11% increase in advance per blast, raising average advance from 2.46 m to 2.82 m and contributing an estimated R1.91 billion in annual net benefit through better ore recovery.
Across multiple sites, operations report up to 80% less flyrock, a 87% improvement in cast, crusher throughput improvements of more than 14%, over $10 million per year in additional value, around $1.45 million in savings from reduced waste, and loading rates improved by as much as 8%.
Gas Bags’ performance is reported chiefly through supplier claims and general air-decking practice rather than detailed, published mine trials. Manufacturers state that properly applied gas bags can reduce explosive consumption by roughly 10-30% while improving fragmentation, thereby reducing downstream crushing costs.
Varistem offers quantified, site-level evidence that it can improve advance, fragmentation, flyrock, cast and crusher throughput, with documented cost and productivity gains across multiple mines. Gas Bag® offers minimal publicly available, independent, mine-specific data linking branded Gas Bag® units to measured improvements in advance, flyrock, or plant performance.
Choose Varistem when you need an everyday stemming solution that tightens confinement without driving your consumables budget out of line. With sizes ranging from 1.75″ to 10″, it’s ideal for small and medium-diameter production holes, allowing staff to achieve consistent collar performance from blast to blast.
If your main challenge is getting more energy into the rock at the collar — rather than sealing water or cavities deep in the hole, Varistem is an ideal choice.
Choose Gas Bags when your problem is deeper in the hole, not just at the collar. Gas Bags are most useful in larger or deeper drill holes where you need a plug that can inflate on its own to hold back water, bridge a cavity or separate explosive layers further down the column.
Each Gas Bag costs significantly more than a basic stemming plug. However, in problem holes, critical rows, or specific patterns, they can deliver benefits.
Varistem and Gas Bags don’t compete for the same job on every blast. Varistem is a low-cost, evidence-backed collar-stemming plug for small- and medium-diameter holes. At the same time, Gas Bags® is a higher-cost, self-inflating borehole plug that is most effective in larger or problem holes. Contact us for a quote to see how your blasting team can benefit from Varistem.
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