BOPA film alone does not block moisture effectively. BOPA film is polyamide, which is inherently hydrophilic. That means BOPA film absorbs water vapor rather than repelling it. At 85% relative humidity, BOPA film can absorb up to 9% of its weight in moisture. Consequently, BOPA film swells and loses dimensional stability. Therefore, for true moisture blocking, BOPA film requires lamination with polyolefins or PVDC coatings.
Compare this to high barrier packaging film. A true high barrier packaging film achieves water vapor transmission rates (WVTR) below 5 g/m²/day. Uncoated BOPA film alone measures 40–60 g/m²/day, which is mediocre. So when engineers ask "Does BOPA film block moisture?", the accurate reply is "Only poorly." However, when coated or laminated, BOPA film becomes part of a high barrier packaging film system. For dry goods, BOPA film must never face moisture alone.
Now consider film for food packaging. Film for food packaging often combines multiple layers to achieve total barrier. Film for food packaging typically uses BOPA as the structural middle layer, with PE or PP as moisture barriers. In this configuration, film for food packaging blocks moisture effectively because the outer layers shield the nylon. Many frozen food bags use film for food packaging with BOPA inside and polyethylene outside. That film for food packaging structure achieves WVTR below 3 g/m²/day.
For demanding applications, high barrier BOPA film solves the moisture problem differently. High barrier BOPA film incorporates a PVDC or SiOx coating directly onto the nylon surface. This high barrier BOPA film reduces WVTR to 1–2 g/m²/day, matching EVOH. High barrier BOPA film is ideal for coffee, spices, and powdered milk. Without high barrier BOPA film, hygroscopic foods would clump and spoil. Therefore, high barrier BOPA film is the correct answer for moisture-sensitive contents.
film for food packaging
high barrier packaging film
high barrier packaging film
What about standard BOPA film? Standard BOPA film is uncoated and unmodified nylon. Standard BOPA film offers zero moisture blocking capability on its own. Standard BOPA film is designed for puncture resistance and aroma barrier, not water vapor defense. If you use standard BOPA film for crackers or cookies, the product will become stale within days. However, standard BOPA film works perfectly inside multilayer laminates where other layers block moisture. Never expose standard BOPA film directly to humid environments.
Returning to the headline question: Does BOPA film block moisture? The complete answer requires nuance. Bare BOPA film blocks moisture poorly due to its hydrophilic chemistry. Standard BOPA film should never be used as a moisture barrier alone. However, high barrier BOPA film with coating does block moisture effectively. As part of a high barrier packaging film system, BOPA contributes strength while companion layers block water vapor. For film for food packaging, BOPA works inside multilayer structures that achieve full moisture defense.
When selecting materials, match the film to your threat. For pure moisture blocking, choose high barrier packaging film with polyolefin skins. For mechanical strength plus moisture defense, specify high barrier BOPA film with PVDC coating. For frozen applications, use film for food packaging that sandwiches standard BOPA film between PE layers. Never rely on uncoated BOPA film alone. Thus, BOPA film blocks moisture only when engineered correctly. Without coatings or laminations, BOPA film fails as a moisture barrier.
Xiamen Changsu Industrial Co., Ltd. (also referred to herein as “Changsu Industrial”) is a worldwide leader in advanced film material manufacturing. Our primary business focuses on Research and Development and intelligent manufacturing of film materials. We own two subsidiary companies: Fujian Changsu Industrial Co., Ltd. and PT Changsu Industrial Indonesia.