Desiccant packaging

What the system does

A permeable sachet lets moisture reach the drying agent. A sealed barrier limits further entry. ThoMar, desiccant method and packaging application

Bounded manufacturer example

Desco's September 2026 TB-2031 gives a reference table for its moisture-barrier-bag system. At 240 square inches of interior bag surface area, the listed minimum is 3.0 desiccant units for maximum interior humidity below 20%, versus 1.5 units below 40%. The target changes the recommendation even though the area is unchanged. Desco TB-2031, p. 2

Desco 13850 contains half a unit per sachet. Those two targets require six and three sachets, respectively. This is packet-count arithmetic, not a shelf-life calculation or a validated dose for another barrier, product or climate. Desco TB-2031, p. 2

A desiccant unit is not a gram or a packet

MIL-D-3464E, dated April 21, 1987, defines a unit by adsorption performance: the quantity of desiccant that, as received, adsorbs at equilibrium with air at 25 °C, at least 3.00 g water at 20% RH and 6.00 g at 40% RH. The mass of desiccant constituting that capacity is its unit weight; the specification limits it to 50 g and requires a manufacturer-defined qualified value. Consequently, “one unit” does not universally mean 28 g, 50 g or one sachet. MIL-D-3464E, §§3.3–3.4, manufacturer-hosted copy

A sachet can contain a fractional unit or several units. Purchase descriptions should identify the capacity designation, material, bag construction, applicable specification and quantity. The specification also distinguishes Type I general-purpose, Type II non-dusting and Type III for specific conditions; those are bagged-product classifications, not names for loose silica gel or clay. Do not infer qualification from a material name alone. MIL-D-3464E, §§1.2 and 3.1

DIN unit designations also require their own test basis. ThoMar explicitly describes DIN 55473 desiccant units as a capacity measure rather than a weight specification. Do not silently substitute another standard's unit or a mass-only sachet when a drawing calls for MIL-qualified units. ThoMar, desiccant-unit explanation

Size for the moisture load and target

A reliable sizing model needs more than empty package volume. ThoMar's application guidance identifies the barrier construction, enclosed dimensions, packing climate, moisture released by the goods and packaging aids, transport/storage climate and duration, and desired final humidity. Wood, cardboard and cushioning can contribute moisture inside a barrier even when the product itself is dry. Longer exposure also allows more moisture to enter through the barrier. ThoMar, calculation inputs

These are sizing inputs, not a universal equation. Excessively wet goods or dunnage may require better preparation rather than more desiccant. Set a product-specific humidity target. ThoMar, calculation inputs and limitations

Barrier, seal and humidity indication

For moisture-sensitive electronics, Desco describes a dry-pack system comprising a moisture barrier bag (MBB), desiccant, humidity indicator card (HIC) and moisture-sensitive identification label. Moisture and ESD requirements must both be addressed where applicable. A bag selected for static control alone does not establish the moisture protection of the complete package. Follow the device-specific dry-packing procedure rather than treating a sachet as a replacement for prescribed drying or exposure controls. Desco Europe, desiccant applications

ThoMar calls for a tightly closed barrier without holes, cracks or faulty closures and insertion of desiccant immediately before closure. Its packaging instructions call for replacing the desiccant after the barrier has been opened before resealing. That is supplier guidance for its packaging method; define a reclosure procedure for the actual system rather than assuming the original protection duration restarts automatically. ThoMar, packaging use

An HIC indicates humidity, not a remaining-capacity percentage. Desco's bulletin describes reversible indicator spots: they continue to change as humidity changes. Read the specified card against its own comparison instructions and applicable acceptance rule. A currently dry indication does not constitute a permanent record of every previous humidity excursion. Likewise, appearance or touch is not a reliable saturation test: Desco notes that its desiccant can remain dry to the touch when saturated. Desco TB-2031, p. 2; Desco Europe, desiccant behaviour

Material choice, placement and reuse

TROPACK distinguishes physically acting materials such as clay, silica gel and molecular sieves from calcium-chloride-based container desiccants. It cautions against direct product contact with the latter and describes them as secondary-packaging materials. Higher advertised water uptake at high humidity is not evidence of better performance at a low-humidity target. Placement also matters: obstructions that slow vapour movement can delay response even where total capacity is sufficient. TROPACK, desiccant FAQ

Reactivation is product-specific. TROPACK gives approximately 150 °C for loose clay or white silica gel, while warning that bags, capsules and cartridges may be damaged by heating; indicator gels have additional limitations. These bulk-material temperatures are not an instruction to bake an assembled sachet. ThoMar states that its industrial desiccant bags are not intended for regeneration. Use an explicitly approved procedure for the exact filled product and wrapper, or replace it. TROPACK, regeneration guidance; ThoMar, regeneration limits

Protect unused stock from humidity. TROPACK ties storage life to the original protective packaging and closure. Record packet identity/capacity, barrier, sealing date, humidity target and intended duration. Verify the complete system; packet count alone cannot establish shelf life. TROPACK, storage guidance

Related reference

Barrier bags · ESD packaging · Delivery guides