Multiwall bags have enjoyed reasonable growth over the last decade by serving the burgeoning pet-food industry. But their place in the packaging pantheon for several markets is under threat.

Multiwall packages are certainly colorful, informative and work well on shelves and display cases. Sizes and shapes have shifted to smaller units so that women, the biggest buyers of pet food, for example, can handle them with ease. The smaller unit size drove the shift from gravure-printing processes to flexography. Still, the traditional markets for multiwall bags, like construction materials and feed & seed, have been steady but not very exciting.

Paper use in all bags is currently under pressure, especially for its two major applications: pet food and bird seed. On the one hand, bird-seed marketers are tired of absorbing costs from bursting bags on retailers' floors. On the other, the Big Box stores are thinking of moving pet food outside in winter months to shelve more profitable apparel. Consequently, the use of woven bags in both applications seems reasonable and maybe more cost-effective.

And that cost is getting more attention now that paper prices are on the upswing. Prices for most grades of kraft (bleached and brown) are up about 25 percent this year due to narrowing supply, steady demand and production (energy, labor) cost increases.

The lower end of the pet-food and seed markets have always used cheap films for cost. These could offer some graphics (up to 2-color) and dimensional stability but were not competitive in quality to multiwall bags. Today though, woven bags, either alone or with a film wrap or facestock, are strongly competing against multiwall. They can be cheaper to buy and offer water resistance and similar strength characteristics as traditional multiwall bags.

It wasn't long ago when woven bags were not popular for anything. They were opaque, poorly formed and not easy to fill or stack due to dimensional instability. They were also manufactured in places such as Central Europe—far away and not very reliable for long-term supply. Made much like fabric, rolls of a synthetic-thread substrate are converted into bags of uniform size and are either printed or laminated with a film or paper cover.

The cost of woven bags to the consumer-product companies has remained steady at around 30-40 cents per unit. Up until recently, this was on par with an unprinted multiwall bag of similar size. In other words, woven bags occupied a small market share in Economy Class. Today, multiwall bags are closer to 60-70 cents each—making woven bags more attractive. Adding a preprinted film or facestock makes woven bags a little more expensive but provides the graphic qualities sought by higher-end buyers.

Woven bags for pet food also have an advantage in water resistance and burst strength. Ink smudges, sagging, sogginess and consequent “no sales” via damage shouldn't be a problem with woven bags stored outdoors.

For bird-seed products, thin-film packaging hasn't been successful due to its lack of strength in unloading, stacking and vermin infestation. Multiwall bags are sometimes used in this application but for indoor storage only. Though the visual impact has made them a better impulse buy, the cost is unsustainable for anything but the occasional buyer. Woven bags, however, provide good dimensional stability, being much harder to rip on impact or burst when dropped (compared to film and multiwall packages).

Most US pet-food plants are located in the South, as are the kraft-paper plants, but projects have begun to re-tool these plants to run woven materials. This is not an easy transition. New woven-bag machinery is also finding its way into domestic locations but from foreign machinery makers.

The first consideration has to be the materials or rollstock. Paper tends to be stiff, rough and pliable—relatively easy to control. Though paper is a bit non-uniform in basis weight and surface, it's more forgiving when new inks or glues are introduced or under changing finishing processes.

Woven materials tend to limp, slide off register and “tunnel,” and break or wrinkle under the wrong tension. A thorough analysis of the materials' tensile strength and tear/tensile index needs review, followed closely by coefficient of friction and stiffness. This will help determine the dimensional stability at printing/laminating. Paper bags rarely have issues with vacuum-fill lines and stand up rather rigidly, while woven bags can be both less porous and less stiff.