CCR Consumables Guide · 2026 Edition
Choosing a CO2 absorbent for your rebreather is not a logistics decision — it is a risk management decision. The choice between absorbent grades forces a calculated trade-off between maximising scrubber duration and minimising the physiological strain of work of breathing. This guide explains what Sofnolime is, what it costs, and how to choose correctly.
The rebreather breathing loop: the diver exhales → gas passes through the scrubber canister → CO2 is chemically neutralised → gas returns to the counterlungs with CO2 removed → O2 is added by the solenoid to maintain the target PPO2 → the diver inhales clean, CO2-free gas. This cycle repeats thousands of times on every dive, and the Sofnolime canister is the critical component that makes it safe.
The chemical composition of Sofnolime 797: approximately 75% calcium hydroxide (Ca(OH)₂), 20% water, 3% sodium hydroxide, 1% potassium hydroxide. This precise mixture is engineered specifically for gas purification in diving applications.
The chemical reaction: CO₂ + Ca(OH)₂ → CaCO₃ + H₂O. The calcium hydroxide is consumed; the CO₂ is converted to calcium carbonate and water. This reaction is exothermic — a warm scrubber canister is a sign of an actively working absorbent. A cold canister after a dive may indicate the canister was not fully utilised — or that channelling occurred and gas bypassed the bulk of the absorbent.
Sofnolime is produced by Molecular Products, a UK-based company with decades of experience in gas purification technology for critical life-support systems — including diving, medical, and military applications. This is not a commodity product; it is an engineered, quality-controlled compound for life-support use.
Why CCR divers cannot substitute generic calcium hydroxide: the specific granule size, moisture content, and chemical balance of Sofnolime 797 is engineered for the gas flow rates and temperature profiles of CCR diving. Generic calcium hydroxide does not have these characteristics and has not been safety-tested in CCR canisters.
The 2–3 kg consumption rate is a baseline at moderate exertion and comfortable water temperature. Cold water increases CO2 production — the body works harder to maintain core temperature — and simultaneously reduces scrubber efficiency (the exothermic reaction proceeds more slowly). Both factors increase actual consumption versus the manufacturer's rated duration.
High-exertion dives — swimming against current, carrying heavy equipment, rapid ascents in heavy seas — produce significantly more CO2 and consume the scrubber faster. Scrubber duration specifications are tested at specific, moderate metabolic equivalent (MET) rates. Exceeding those rates reduces real-world duration proportionally.
The rule most experienced CCR divers follow: change Sofnolime before every dive regardless of the previous dive's duration. The $6–$12 cost of fresh absorbent is not worth the risk of a partially spent canister on your next dive. There is no reliable way to assess how much residual capacity remains in used Sofnolime.
Annual cost in the full TCO calculation: factor $300–$600 Sofnolime cost into your total annual running costs alongside O2 sensor replacement, O2 fills, and annual servicing. Use our TCO Calculator to model your specific dive frequency and conditions.
Work of Breathing (WOB) is the physiological effort required to move gas through the breathing loop. Higher WOB increases respiratory muscle fatigue, accelerates CO2 production, and — on demanding dives — can contribute to hypercapnia risk. It is a real and measurable physiological cost, not a comfort preference.
Granule size and WOB: smaller, more angular granules (like those in some absorbent grades) pack more tightly, creating greater resistance to gas flow and higher WOB. Larger, more spherical granules pack less densely, reducing resistance — but may offer less reactive surface area in the same canister volume, explaining the shorter duration.
| Factor | Sofnolime 797 | Spherasorb |
|---|---|---|
| Mean scrubber duration (6 MET) | 202 minutes | 138 minutes |
| Work of breathing | Baseline | ~10% lower |
| Manufacturer approval | Most CCRs | Check manufacturer |
| Best for | Long dives, cave, deco | High-exertion, shorter dives |
| Duration reduction if substituting | Reference | Up to 2/3 reduction vs Sofnolime |
The practical implications: for long, cold-water decompression dives or extended cave penetrations, Sofnolime's 202-minute mean duration provides a greater safety margin. The additional 64 minutes of rated duration versus Spherasorb can be the difference between a controlled ascent and an emergency on a 150-minute planned dive profile.
For high-exertion dives where WOB fatigue is the limiting factor, Spherasorb's 10% reduction in breathing resistance may reduce CO2 production risk. But this gain comes with a dramatically shorter rated duration — a trade-off that must be explicitly accounted for in dive planning.
Critical warning from Martin Parker / AP Diving: "When using alternative CO2 absorbents, usage times may need to be reduced to less than one-third of the time specified for Sofnolime 797." At 202 minutes Sofnolime duration, this implies no more than approximately 67 minutes on an unapproved alternative. Using an alternative absorbent without understanding the manufacturer's adjusted duration limits is a serious safety risk.
Duration specifications published by manufacturers are determined through controlled testing with a specific absorbent at specific conditions. Using a different product without understanding how it alters duration means operating outside the tested envelope — without knowing by how much, or in which direction the risk changes.
TDI, IANTD, and PADI all teach that manufacturer guidance on absorbent selection is a core safety principle, not a commercial preference or brand loyalty issue. The training curriculum teaches this as fact because the underlying safety data supports it.
The AP Diving warning quantifies the potential risk concretely: alternative absorbents may require duration reduction to less than one-third of the Sofnolime 797 specification. At 202 minutes Sofnolime duration, this implies a maximum of approximately 67 minutes on an unapproved alternative. An experienced diver who plans a 2-hour cave penetration without accounting for this could face scrubber failure mid-penetration — with no direct path to the surface.
The safest approach is also the simplest: use what your unit was tested with. For the vast majority of CCR systems, this is Sofnolime 797.
Channelling explained: gas follows the path of least resistance. In a loosely packed canister, it creates a channel through the absorbent rather than flowing uniformly through the entire granule bed. The result: a diver experiences CO2 breakthrough with most of the Sofnolime still visually unused. The spent granules at the channel are exhausted; the rest of the canister never activated.
Handle Sofnolime carefully. The granules are fragile — rough handling creates fine dust that increases WOB and poses an inhalation hazard. Use gloves: the calcium hydroxide is caustic on skin with prolonged contact. Store Sofnolime in sealed containers in cool, dry conditions. Opened bags degrade from atmospheric CO2 and humidity. Never leave an opened bag unsealed between dives.
Specialist dive retailers: technical diving supply shops that serve CCR divers stock Sofnolime 797 in the correct grade. Staff can confirm compatibility with your specific unit. For consumables restocking, building a relationship with a local technical dive shop saves time and ensures you're always getting the correct product.
Amazon: Sofnolime is available on Amazon UK — useful for consumable restocking. Confirm the product listing specifies Sofnolime 797 or the grade your manufacturer specifies. Do not purchase based on price alone — verify the grade.
View Sofnolime on Amazon UK →Expedition planning: for remote dive trips, calculate your required Sofnolime volume before departure. At 2–3 kg per dive and 20 dives on a two-week liveaboard, that is 40–60 kg of absorbent — a significant logistics consideration. The higher duration of Sofnolime 797 versus alternatives makes it the preferred choice when carrying capacity is limited. Plan and pre-order before travelling to regions without specialist dive supply infrastructure.
Cannot find it locally: check with your local technical dive shop — most shops serving CCR divers stock or can order Sofnolime 797. Some CCR manufacturers also sell absorbent direct.
Sofnolime is a granular calcium hydroxide-based CO2 absorbent used in the scrubber canister of a closed-circuit rebreather (CCR). As the diver exhales, gas passes through the scrubber canister where the Sofnolime chemically reacts with and neutralises carbon dioxide, preventing the buildup of CO2 in the breathing loop. Without functioning CO2 scrubbing, the diver would experience hypercapnia within minutes.
A typical CCR dive at moderate exertion consumes approximately 2–3 kg of Sofnolime. At approximately $3–$4 per kilogram in the US market, this works out to $6–$12 per dive in absorbent cost alone. Most experienced CCR divers use fresh Sofnolime for every dive as a non-negotiable practice.
Sofnolime 797 is the most widely used grade of Sofnolime for recreational and technical CCR diving. It has been extensively tested by major CCR manufacturers including AP Diving, Hollis, and JJ-CCR, and is the reference absorbent for most manufacturer-published scrubber duration specifications. Most CCR training agencies recommend using the absorbent grade used to test and certify your specific unit — for most units, this is Sofnolime 797.
No. Sofnolime cannot be reused after a dive. The chemical reaction with CO2 is irreversible. Attempting to reuse spent Sofnolime is extremely dangerous and has caused fatalities. Most experienced CCR divers change their Sofnolime before every dive regardless of the previous dive's duration.
Independent scientific testing at 6 MET found a mean scrubber duration of 202 minutes for Sofnolime versus 138 minutes for Spherasorb — a 46% duration advantage for Sofnolime. However, Spherasorb produced 10% less work of breathing (WOB) resistance. For long cave or decompression dives, Sofnolime's duration advantage is typically more important. Always check your manufacturer's approved absorbent list before substituting.
Our Total Cost of Ownership Calculator includes a Sofnolime cost-per-dive input. Model your complete CCR running costs before you buy.
⚠ Not diving instruction. Always use manufacturer-approved absorbents. Certified training required before diving any CCR system.