Aquacel Ag and calcium alginate are not the same product. They look similar, come in similar forms (flat sheets and ribbon for packing), and both absorb wound drainage, which is why they’re often confused. But they’re made from completely different materials, handle fluid differently, and serve somewhat different purposes in wound care.
What Each Dressing Is Made Of
Aquacel Ag is built from sodium carboxymethylcellulose (CMC) fibers, a technology its manufacturer ConvaTec calls Hydrofiber. These are plant-derived cellulose fibers that have been chemically modified to absorb large amounts of fluid. The “Ag” stands for silver: Aquacel Ag contains 1.2% ionic silver by weight, which releases slowly into the wound to reduce bacterial growth. The silver remains active over several days, though the highest release happens in the first 24 hours.
Calcium alginate dressings, by contrast, are made from alginic acid derived from brown seaweed. When the seaweed-based fibers contact wound fluid, they exchange their calcium ions for sodium ions in the fluid, turning the fibers into a soft gel. This ion exchange is what gives calcium alginate its unique clotting ability. Standard calcium alginate dressings do not contain silver, though some manufacturers offer silver-containing alginate variants as separate products.
How They Handle Wound Fluid
This is one of the most important practical differences between the two. Aquacel Ag absorbs fluid vertically, pulling it straight up into the fiber structure. The fluid stays locked in the area directly over the wound and does not spread sideways across the dressing. This vertical-only absorption helps protect the healthy skin around the wound from becoming waterlogged and breaking down, a problem clinicians call periwound maceration.
Calcium alginate dressings also have strong absorption, but fluid can wick laterally, spreading outward across the dressing. In lab testing, calcium alginate dressings absorbed more than 35 grams of blood per 100 square centimeters of dressing, compared to about 20 grams for Aquacel. So alginates absorb a greater total volume, but that fluid can spread sideways and potentially irritate surrounding skin. For heavily draining wounds where maceration is already a concern, the way Aquacel contains fluid may matter more than raw absorption capacity.
Clotting Ability
Calcium alginate has a clear advantage when it comes to bleeding wounds. The calcium ions in the dressing actively promote blood clotting through two mechanisms: they concentrate blood cells at the wound surface, and they trigger part of the body’s natural clotting cascade. This makes calcium alginate a true hemostatic agent, useful for wounds that bleed during dressing changes or surgical sites where minor bleeding is expected.
Aquacel Ag does not have this hemostatic property. It absorbs blood like any absorbent dressing, but it doesn’t actively accelerate clot formation. If a wound bleeds significantly, calcium alginate is the better choice for that reason alone.
Antimicrobial Protection
The silver in Aquacel Ag gives it antimicrobial properties that plain calcium alginate lacks. Ionic silver disrupts bacterial cell walls and interferes with bacterial reproduction, helping manage wounds that are infected or at high risk of infection. This is particularly relevant for chronic wounds like diabetic foot ulcers or venous leg ulcers, where bacteria can stall healing for weeks.
One consideration with silver dressings: some patients develop skin sensitivity to silver compounds, and there is ongoing discussion about whether prolonged silver use can contribute to bacterial resistance. Plain calcium alginate avoids both of these concerns. If a wound isn’t infected and doesn’t have significant bacterial burden, the antimicrobial component may not be necessary.
When Each Dressing Works Best
Choosing between these dressings comes down to what the wound needs most at that point in healing.
- Moderate to heavy drainage with infection risk: Aquacel Ag is well suited here. Its vertical absorption protects surrounding skin, and the silver addresses bacterial concerns.
- Bleeding wounds or surgical sites: Calcium alginate is the stronger choice because of its hemostatic properties.
- Heavy drainage without infection: Plain calcium alginate (or plain Aquacel without silver) handles high fluid volumes effectively. Alginate absorbs more total fluid per area of dressing.
- Wounds with fragile surrounding skin: Aquacel’s resistance to lateral wicking makes it preferable when the skin around the wound is already compromised or at risk of maceration.
Both dressings form a gel as they absorb fluid, which keeps them from sticking to the wound bed and makes removal less painful. Both can be used in flat sheets over surface wounds or packed as ribbon into deeper cavities and tunneling wounds. Both require a secondary dressing on top to hold them in place. Despite these similarities in form and function, they are fundamentally different materials with distinct strengths, and treating them as interchangeable can mean missing the specific benefit your wound actually needs.