Calcium Chloride (CaCl2) — DunLash Ultra
Calcium chloride is a hygroscopic salt that absorbs moisture from the air and converts it into a calcium chloride solution — a gel that is locked inside the desiccant bag. CaCl2 desiccants continue absorbing moisture as long as conditions remain above the saturation point, meaning they remain effective throughout long voyages with multiple dew-point cycles.
DunLash Ultra 750g contains 625g of CaCl2 at 95% purity plus natural fibre. It is manufactured by IDS International and distributed by DunLash Systems across South Africa.
Clay Desiccant (Montmorillonite) — PacDry
Montmorillonite clay is a naturally occurring mineral that adsorbs moisture into its crystal structure. It is chemically inert, low-cost, and effective at lower humidity levels. However, clay desiccants reach saturation at a lower absorption level than CaCl2 products and — critically — release moisture back into the air when temperature rises. This makes clay less effective for container applications where temperature cycling is significant.
DunLash PacDry is a montmorillonite clay primary desiccant sized in desiccant units per US MIL-D-3464E. It is recommended for primary packaging applications — small enclosed spaces such as instrument cases, electronics packaging, and sealed cartons — rather than the large air volume of a 20ft or 40ft shipping container.
Silica Gel
Silica gel is the most widely known desiccant type, familiar from the small sachets in footwear, electronics, and pharmaceutical packaging. Like clay, silica gel adsorbs moisture physically rather than chemically. It reaches saturation at relatively low absorption levels (typically 20–30% of its own weight) and releases moisture when temperature rises — the same limitation as clay when used in container applications with significant temperature cycling.
Silica gel is well-suited to small, temperature-stable enclosed spaces. For large container air volumes and voyages with significant temperature variation, it does not provide the sustained absorption performance that CaCl2 desiccants deliver.
Absorption Performance — The Numbers
DunLash Ultra has been independently tested against competitor desiccant products under controlled conditions replicating real container voyage humidity and temperature profiles. The test data compares absorption performance at 30°C across humidity profiles from 70% to 90% relative humidity — the range encountered in containers during typical ocean voyages from South Africa.
| Test Condition | DunLash Ultra 750g |
|---|
| 30°C / 80% RH | Absorbs up to 250% of bag weight |
| 30°C / 90% RH | Absorbs up to 300% of bag weight |
| 28°C / 70% RH | Absorbs up to 150% of bag weight |
| Temperature cycling (30°C – 70°C profile) | Retains absorbed moisture as gel — does not re-release |
The critical finding: DunLash Ultra 750g delivers greater total moisture absorption than a competitor product weighing 1.1kg — 47% heavier. The advantage is most pronounced at the higher humidity levels (80–90% RH) that are most damaging to cargo — precisely the conditions encountered when containers are packed in humid coastal environments or cross the equator.
The Re-release Problem — Why It Matters for Container Voyages
For short, temperature-stable storage applications, all three desiccant types perform adequately. The critical difference emerges during sea voyages with significant temperature variation.
Clay and silica gel desiccants adsorb moisture physically. When the temperature rises — which happens every day as the container warms during daylight, and more significantly when the vessel moves between climate zones — the absorbed moisture is partially released back into the container air. This means a clay or silica gel desiccant that absorbed moisture during the cool night cycle releases it again during the warm day cycle. The net moisture removal is far lower than the raw absorption capacity suggests.
DunLash Ultra CaCl2 does not have this problem. The calcium chloride reacts chemically with absorbed water, locking it as a gel. This reaction is not significantly reversed by temperature increases within the range encountered in standard sea voyages. The moisture absorbed stays absorbed for the duration of the voyage.
Which Desiccant for Which Application?
| Application | Recommended DunLash Product |
|---|
| 20ft or 40ft GP container — sea freight | DunLash Ultra 750g |
| Reefer container | DunLash Ultra 750g |
| Primary packaging — electronics, instruments | PacDry (Montmorillonite clay) |
| Primary packaging — pharmaceuticals | PacDry or silica gel |
| Long-haul road freight in sealed containers | DunLash Ultra 750g |
| Short-haul road freight, low humidity | PacDry or lower-spec option |
Cost Per Container — A Realistic Comparison
Some buyers choose clay or silica gel because the per-unit purchase price is lower. This comparison changes when evaluated on a per-container, per-voyage basis:
- DunLash Ultra absorbs up to 250% of its weight. A standard 40ft container requires 8 x 750g bags = 6kg of DunLash Ultra, capable of absorbing up to 15kg of water.
- A clay desiccant bag rated at equivalent absorption would need to weigh significantly more than 750g to match this performance — and would still release a portion of its absorbed moisture during temperature cycling.
- The cost of a single damaged container — even a partial loss — typically far exceeds the cost saving of using a lower-performing desiccant. One mould claim, one corroded shipment, or one label-damage rejection at destination erases many months of desiccant cost savings.
Why Choose DunLash for Container Desiccant Protection
DunLash supplies moisture control and cargo protection products for South African exporters, freight forwarders, agricultural producers, packhouses, logistics companies, and food cargo operators. Our solutions help protect cargo from condensation, container rain, mould growth, packaging collapse, corrosion, and moisture-related claims during road, rail, and ocean freight.
DunLash can assist with desiccant dosage recommendations based on cargo type, container type, voyage duration, route profile, pallet moisture, and specific export requirements.
