Why can silicone membranes be breathable but not bacteria-proof?

Those who have used silicone foam dressings or silicone tape may have noticed that these dressings don't breathe well when applied to wounds. Could this lack of breathability cause suffocation? However, in actual use, silicone films do allow the skin to breathe normally while keeping bacteria out. The principle is not complicated; the key lies in pore size control and the hydrophobic properties of the material itself.

Aperture is the core threshold

The size of bacteria makes it difficult for them to pass through the micropores of ordinary medical materials. Common Staphylococcus aureus has a diameter of about 0.5 to 1 micrometer, while Escherichia coli is about 1 to 2 micrometers long and about 0.5 micrometers in diameter. Silicone membranes can block bacteria because their micropores are designed to be smaller than the size of bacteria. A study on microporous silicone membrane double-layer dressings showed that the pore size of the upper small-pore silicone membrane is much smaller than the diameter of bacteria, effectively preventing bacterial invasion. It's like a sieve with pores smaller than sand; the sand naturally can't pass through.

Silicone films are hydrophobic, making it difficult for water molecules to pass through. However, water vapor molecules are much smaller than liquid water molecules and can pass through the gaps between the molecules of the material to evaporate. This property prevents exudate from accumulating under the dressing and also prevents the wound from being contaminated by external bacteria. Simply put, bacteria can't get through, but water vapor can escape.

Bi-layer design for aperture distribution

Some silicone membrane dressings employ a dual-layer structure to optimize performance. The upper layer is a small-pore silicone membrane with precisely controlled pore sizes that bacteria cannot pass through, while ensuring adequate water vapor permeability. This effectively blocks external bacterial invasion without making the wound too moist. The lower layer is a large-pore silicone membrane; the larger pores facilitate cell adhesion and proliferation, promoting the growth of granulation tissue and epithelial cells. This design separates protection and healing promotion into two distinct layers, each fulfilling its specific function. 

How to specifically measure breathability?

The breathability of silicone films is quantified in industry by a measure called water vapor transmission rate. For a qualified material, this value is typically in the range of several hundred grams per square meter per day. This means that sweat in the area covered by the dressing can continuously evaporate without trapping on the skin. Medical silicone dressings are explicitly required to have breathability and exudate absorption capabilities in their registration standards. This is why patients rarely report skin irritation after applying silicone films in actual use.

Two common misconceptions in daily use

Some people believe that the tighter the silicone mask is applied, the better, and they stretch it forcefully before applying it. This will cause the skin to be under continuous horizontal tension, which can easily lead to blisters or tension injuries. The correct way is to place the dressing flat on the skin and smooth it out from the center outwards, without stretching it.

Another misconception is rushing to change the dressing as soon as it turns white. Silicone foam dressings usually turn white because they have absorbed exudate, which is normal. As long as the dressing isn't leaking, the edges aren't curling up, and the surrounding skin isn't red or swollen, it can continue to be used. Removing it prematurely can actually interfere with the newly formed tissue.

For more information on Innomed® Silicone Foam Dressing, refer to the Previous Articles. If you have customized needs, you are welcome to contact us; You Wholeheartedly. At long-term medical, we transform this data by innovating and developing products that make life easier for those who need loving care. 

Editor: kiki Jia