Kollder vs I-CWIK: Cold Water Immersion System Comparison

The I-CWIK (Ice-Cold Water Immersion Kit) by Nereus Medical is one of the most widely deployed cold water immersion systems in military and sporting event medicine, particularly in English-speaking markets. Here is an objective comparison with Kollder, based on publicly available product specifications and international protocol requirements.

Product overview

I-CWIK is a flexible PVC bag with YKK AQUASEAL® waterproof zips, designed by Dr Ross Hemingway OBE for Nereus Medical (UK). Lightweight and portable, it is used by military medical teams, rescue services and sporting event organisations in several countries.

Kollder is an emergency cooling tub with a food-grade stainless steel frame and high-resistance liner, engineered for rapid prehospital deployment by one person, with full patient access during immersion.

Technical comparison

What the I-CWIK does well

Portability. The I-CWIK system is extremely lightweight and compact. It can be carried in a backpack or in the smallest vehicle, making it a popular choice for teams operating under extreme logistical constraints (military patrols, mountain rescue).

Rapid deployment. The bag deploys quickly with no frame to assemble — this is its primary advantage over rigid frame systems.

Material quality. The YKK AQUASEAL® zips and PVC durability are well-documented strengths.

The fundamental limitation of the I-CWIK: patient access

The critical issue with the I-CWIK is its closed-bag design. Once the patient is immersed, the bag is closed around them — which significantly limits or prevents advanced medical procedures during cooling.

Yet medical recommendations are explicit: during immersion of an exertional heat stroke patient, the medical team must be able to:

• Continuously monitor the airway — a severely hyperthermic patient may experience seizures, vomiting or sudden loss of consciousness
• Measure rectal temperature every 5 minutes to determine when to stop cooling
• Insert an IV line if required
• Perform cardiopulmonary resuscitation in the event of secondary cardiac arrest

The IOC consensus (Hosokawa, Racinais et al., BJSM 2021) and ACSM guidelines clearly state that continuous monitoring and access to medical procedures are non-negotiable components of the protocol.

Nereus Medical's own documentation states: "Persons should be monitored continuously when cold water immersion treatment is being performed with the I-CWIK. Under no circumstances should patients be left unattended due to the risk of drowning and death."

The protocol validation question

The I-CWIK claims cold water immersion capability — which is accurate. But the international reference protocol (CWI) specifies whole-body immersion, scalp included, with the airway maintained above water by attending medical staff. This active monitoring is difficult to sustain with a closed bag.

Medical teams at major competitions and military medical officers who regularly perform prehospital immersions raise this point: the ability to intervene at any moment during immersion is non-negotiable for severe cases.

Conclusion

The I-CWIK is a useful tool for teams operating under extreme logistical constraints and managing mild-to-moderate hyperthermia cases. Its portability is a genuine advantage.

For severe exertional heat stroke — precisely the situations where cooling equipment is critical — the reference protocol requires full patient access during immersion. Kollder meets this requirement without compromising portability or deployment speed.

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I-CWIK data: nereusmedical.com (public product documentation). Protocol data: ACSM Expert Consensus Statement 2023, IOC Adverse Weather Impact Expert Working Group Tokyo 2020 (Hosokawa, Racinais et al., BJSM 2021).