ENGLISH
Understanding the mechanisms, evaluating solutions, and choosing the right approach for your environment
Published by So Sponge — February 2026
Executive Summary
IP65+ enclosures protect electronic equipment against liquid water, but not against moisture in vapour form. When subjected to temperature variations, any sealed volume progressively accumulates humidity through thermal cycles — potentially causing condensation, corrosion, and electronic failures.
In response to this reality, several families of solutions exist: traditional desiccants (silica gel), vents and depressurisation membranes, internal heating systems, and protective coatings. Each presents optimal use cases and specific limitations.
This document offers a neutral, comparative technical analysis of these approaches, specifying the conditions under which each is relevant. It then introduces dynamic humidity management materials — including the SRD technology developed by So Sponge — as a complementary response suited to certain demanding configurations.
This white paper is published by So Sponge, developer of the SRD technology. We have taken care to present the merits and limitations of each solution in a balanced manner. The reader is invited to evaluate the information in light of their own use case.
Chapter 1
An enclosure rated IP65 or above guarantees protection against liquid water in accordance with the IEC 60529 standard. This level of protection is often mistakenly interpreted as protection against all forms of moisture. However, the IP rating does not cover water vapour.
In any sealed volume subjected to temperature variations — day/night cycles, heat generated by electronic components, transportation — the internal air expands and then contracts. These pressure variations induce air exchanges with the exterior via seals, membranes, or micro-leaks. With each cooling cycle, water vapour is introduced and the internal relative humidity increases.
Beyond 60% relative humidity (RH), the risks of corrosion, leakage currents, and electronic failures increase significantly.
The more an enclosure is sealed against liquid water, the more it behaves as a thermal trap: water vapour accumulates cycle after cycle. The level of protection thus becomes an aggravating factor in the absence of active management of internal moisture.
The effects of moisture on electronic systems manifest through several distinct mechanisms:
On cold surfaces and electronic circuit boards, which can cause direct short circuits.
Of tracks, connectors, and solder joints through electrochemical reaction.
Between adjacent tracks, impairing circuit performance.
On organic substrates present within the enclosures.
Of seals, weakened by repeated cycles of humidification and drying.
Above 60% RH, battery self-discharge doubles.
Chapter 2
The engineer has several tools available to control humidity within an IP65+ enclosure. These approaches are not mutually exclusive — a combination is often necessary depending on the application's constraints.
Silica gel is the most widely used and best-documented solution. It is particularly effective in the following configurations: stable-temperature environments, indoor applications, systems subject to planned maintenance, and storage or transport phases.
Its limitations become critical in thermally unstable environments: very low residual capacity beyond 50% RH, irreversible saturation without external heating, and progressive drift in the absence of regeneration.
Breather vents allow pressure to be equalised whilst maintaining the IP classification with respect to liquid water ingress. They are indispensable for the mechanical management of pressure, but have no desiccant effect: the interior converges towards the external ambient humidity.
Internal heating is effective but energetically costly, and is incompatible with battery-powered systems. Conformal coatings constitute a useful last line of defence but do not address the hygrothermal cause. These solutions are ideally combined with the preceding approaches for high-criticality applications.
The limitations of the "IP65 enclosure + static silica gel" combination in thermally unstable environments have led to the exploration of materials capable of managing moisture flux in phase with the system's thermal cycles.
These so-called dynamic humidity management materials exhibit a significant hysteresis between adsorption and desorption. The SRD technology from So Sponge falls within this category.
A new generation of materials capable of adapting to thermal cycles and maintaining active protection in the most demanding environments.
Chapter 3
This section provides a factual comparison between classic silica gel and SRD technology, including configurations where silica gel remains the most appropriate choice.
The graph below illustrates the behaviour of both materials across the full range of relative humidity. The red zone (70–100% RH) corresponds to the critical range for electronic reliability.
Figure 1 — Compared adsorption curves: Silica Gel vs SRD (So Sponge). The red zone marks the critical range (70–100% RH).
Silica gel reaches the majority of its absorption capacity between 0 and 50% RH. Beyond this, its residual capacity is approximately 0.1 g of water per gram of material — insufficient to buffer hygrothermal shocks. SRD technology, by contrast, exhibits a near-exponential capacity beyond 50% RH, capable of reaching 0.8 g/g during condensation peaks.
In the 50–100% RH range, SRD's additional absorption capacity is approximately 8 times greater than that of silica gel. This difference is decisive in enclosures subjected to significant thermal cycling where condensation is possible.
The diagram below illustrates the central mechanism of SRD technology: the hysteresis between adsorption and desorption allows the material to partially regenerate with each thermal cycle, without any external intervention — unlike Silica Gel, which inevitably reaches saturation over successive thermal cycles.
Figure 2 — Spontaneous operating cycle of SRD in an IP65+ enclosure subjected to thermal variations.
Subjected to daily thermal cycles, silica gel can reach its maximum adsorption capacity within a few weeks. With no possibility of regeneration, the internal relative humidity drifts inexorably towards 100% RH — the condensation threshold — and remains there. SRD, by contrast, exploits each daily thermal peak to desorb spontaneously, maintaining internal humidity at 60 ± 15% RH. No saturation, no intervention.
Figure 3 — Hygrometric drift of saturated silica gel vs SRD stability over 90 days of thermal cycling (ΔT = 40°C/day).
Chapter 4
The diagram below presents a decision tree to identify the most appropriate solution based on the characteristics of the enclosure and its environment.
Figure 4 — Decision tree: selection of the humidity management solution according to the application context.
1
Silica gel sized according to best practice remains the robust and economical solution.
2
The combination of silica gel and a vent provides satisfactory protection.
3
The SRD represents the most suitable approach.
4
The combination of conformal coating and heating remains the reference solution regardless of cost.
Humidity management in IP65+ enclosures is not a one-size-fits-all problem. Each approach — silica gel, vents, heating, coatings, dynamic materials — has its own domain of relevance.
Silica gel remains a valid and economical solution for many applications in controlled environments with plannable maintenance. So Sponge's SRD technology addresses a specific need: maintaining an active hygrothermal regulation capacity in systems subjected to significant thermal cycling, where silica gel becomes saturated before it can fulfil its protective role.
It is not positioned as a systematic replacement for existing solutions, but as an adapted response to the most demanding use cases.
So Sponge supports its partners in evaluating the most suitable solution: thermal cycle analysis, sizing, and comparative testing.
Contact us at guirec@sosponge.com for a personalised assessment.
1. IEC 60529: Degrees of protection provided by enclosures (IP Code).
2. AGM Container Controls — Engineering Moisture & Pressure Protection Guide.
3. Vikinor — Preventing Condensation in Sealed Enclosures.
4. Canadian Conservation Institute — Silica Gel and Relative Humidity.
5. Australian Inhibitor — Calculating Desiccant Storage Requirements.
6. Danfoss — Application Note AB501642557477: Pressure Equalisation Elements.
7. So Sponge — Comparative Analysis: Silica Gel vs SRD Technology for IP65+ Enclosures, 2025.
8. PMC / NCBI — Adsorption and desorption characteristics of silica gel under cyclic humidity conditions.
The guide "Managing Humidity in IP65+ Enclosures" is now available. The So Sponge team wishes you happy reading!
READ THE GUIDE NOW