What Material Can Be Used for Small Tea Sachets To Provide Moisture And Light Protection While Effectively Locking in The Aroma?

A Bag of Longjing That Lost Its Soul

A client of ours who makes small tea sachets told me a story I haven't forgotten. He exports primarily to Japanese and European tea brands. Last year, he shipped a batch of pre-Qingming Longjing green tea to Japan, packed in standard kraft paper metallized bags. When the client on the other end opened a sachet and brewed it, the feedback was blunt: "The aroma is flat. There's a stale-paper smell." He was puzzled — the seal was fine, no extreme heat during transit. What went wrong?

He tested the moisture content. It had risen 1.8 percentage points above the factory spec. The problem lay in that "metallized" layer. The aluminum coating on kraft paper base film is only 0.03-0.05 microns thick — nowhere near enough to block water vapor. And the metallized layer's light transmittance exceeds 5%, letting UV in to degrade chlorophyll and volatilize aroma compounds. To make matters worse, kraft paper itself migrates odors — that "stale paper" smell came straight from the bag material.

What he actually needed was a material that could solve moisture, light, and aroma retention all at once. The answer turned out to be aluminum-plastic composite film.

Three Threats Inside Every Tea Sachet

Tea is one of the most temperamental products in all of food packaging. Three enemies: moisture, oxygen, and light.

Moisture: Green tea at 80% relative humidity can absorb 5% of its own weight in water within just 24 hours. That triggers "tea bloom" — the dull oxidation layer on the surface that flattens aroma and deadens flavor. Industry standard for tea packaging is WVTR below 0.5 g/m²·day. For export shipments crossing tropical shipping lanes over 45-day container transit, the requirement drops to 0.2 or lower.

Oxygen: Tea polyphenols and pigments oxidize in the presence of oxygen, darkening the liquor and flattening the aroma profile. Unfermented green teas are especially vulnerable. Research shows that unprotected premium green tea can lose 15-30% of its aroma compounds within three months at room temperature.

Light: UV is the killer. It breaks down chlorophyll (green tea turns yellow), destroys aromatic compounds (aroma disappears), and accelerates lipid oxidation (producing that "stale" off-note). Light transmittance needs to stay at 5% or below — for premium teas, even lower.

Standard packaging — plain PE bags, kraft paper bags, metallized film — can only block one or two of these threats. Only aluminum foil laminate blocks all three completely.

PET/AL/PE: The Gold Standard Structure for Tea Sachets

Three layers, each doing its own job, combined performance far exceeding the sum of parts.

Outer PET layer (12 microns): Provides mechanical strength and the printing surface. High tensile strength, abrasion resistance, and a smooth surface ideal for high-quality printing. Tea brands need beautiful graphics and brand information on small sachets — PET is the best substrate for that.

Middle aluminum foil layer (7-9 microns): This is the core. Even at just 7 microns, aluminum foil delivers near-zero oxygen transmission, WVTR below 0.5 g/m²·day, and complete light opacity. Moisture can't get in. Oxygen can't get in. Light can't get in. The tea inside the sachet essentially sits in suspended animation.

Inner PE layer (50-80 microns): Handles heat sealing and food contact safety. Food-grade LDPE or LLDPE, seals cleanly at 120-140°C, no leaks, no odor migration.

How effective is this structure? Green tea packed in PET/AL/PE achieves 18-24 month shelf life. The same tea in a plain PE bag? Two to three months. The difference is staggering.

Why Small Sachets Need Foil Laminate Even More

Large-format tea gets opened and consumed quickly. Small sachets are different. Each one holds just 5-8 grams, and from production to the consumer's cup, it might sit for months — even half a year. Each sachet is its own tiny microenvironment. If any single layer of protection fails, that one sachet is wasted.

And the surface-area-to-volume ratio of small sachets is far larger than bulk packaging. The same 500 grams of tea: a few surfaces in a large bag, but hundreds of individual sachets — total contact area multiplied several times over. Permeation risk scales up accordingly. The absolute barrier capability of aluminum foil becomes magnified in this small-sachet context.

Then there's the heat seal. Small sachets mean short seal edges and high-speed operation. The PE layer's heat-sealing consistency becomes critical. If the PE melting range is too narrow or too wide, you get weak seals or burnt seals on the high-speed line. A well-engineered foil laminate selects PE grades with matching melt characteristics, ensuring every single sachet hits target seal strength at 300-400 bags per minute.

VWIN's Aluminum-Plastic Composite Film for Tea Packaging

VWIN supplies aluminum-plastic composite film to multiple tea brand clients, using the classic PET/AL/PE structure with aluminum foil layer at 7-9 microns (selectable), WVTR below 0.5 g/m²·day, and oxygen transmission approaching zero. We support custom widths and roll diameters to match various automatic tea sachet packing machines. Every shipment includes OTR, WVTR, and heat seal strength test data from actual production runs.

If you're struggling with freshness retention in your tea sachets, or want to upgrade your current packaging material, get in touch. We can provide samples and a technical comparison.