Static Protection and Moisture Protection Are Different Jobs
The layers in a packaging stack
A typical electronics pack has three functional layers. The inner contact layer cushions and, where required, provides a static-dissipative surface. The shielding layer, usually a metallised bag, forms a Faraday enclosure that protects the contents from external fields. The outer moisture barrier, where used, is a foil structure with a low moisture vapour transmission rate, paired with desiccant and a humidity indicator.
The common error is treating these as substitutes. A metallised shielding bag is not a moisture barrier; humidity passes through it. A foil moisture barrier bag is usually not the right contact surface and is often not rated for repeated handling. Using one layer to do both jobs produces a pack that fails one of them.
Deciding whether you need dry pack
A moisture barrier is needed where the part is moisture sensitive and the transit or storage period is long enough for ambient humidity to matter, or where condensation during transport is a real risk. Where the part is not moisture sensitive, adding a barrier bag adds cost and a desiccant handling step without a protective benefit.
If dry pack is specified, specify it completely: the moisture sensitivity level the pack is designed for, the desiccant quantity, the indicator card, and the floor-life rule after the bag is opened. A barrier bag and desiccant with no stated floor life leaves the receiving line guessing, and the usual result is that the bag is opened early and left open.
FAQ
Is a shielding bag also a moisture barrier?
No. Metallised shielding bags protect against static fields but transmit moisture. Moisture protection needs a foil barrier structure.
When is dry pack needed?
Where the part is moisture sensitive and transit or storage is long enough for humidity to matter, or where condensation in transit is a risk.
What must a dry pack specification include?
The moisture sensitivity level being addressed, desiccant quantity, indicator card, and the floor life after the bag is opened.
What is the inner layer for?
Cushioning and, where required, a static-dissipative contact surface. The foil barrier is normally not a suitable contact layer.
All figures above refer to standard product data sheets; final confirmation is subject to written quotation.