The Sofnolime Pages

information and pricing

NOTICE . . . Northwood Designs,  Inc. no longer distributes sofnolime.

Sofnolime is a high quaility absorbant, with very little dust.  It also comes with a chemical indicator which changes color as the material abosorbs CO2.

General Information Specific Characteristics Granule size Distribution
Storage of Sofnolime Transport of Sofnolime Personal Protection
Disposal Which mesh size to use?


General Information

    "Sofnolime" is the trade name of a brand of Soda-lime made by Molecular Products Ltd. in Thaxted, UK.   It is designed to be used in a variety of applications but includes special characteristics that make it one of the best CO2 absorbants for use in rebreathers.  Do not confuse this with some grades not rated for use in a rebreather.

    Sofnolime is a specially prepared mixture of calcium and sodium hydroxides.  The granules are creamy white in color, hard and processed to minimise dust formation. It is also porous, and irregularly shaped to provide for a larger surface area.

    When put in contact with a acidic gas like CO2, a strong, exothermic (heat producing) reaction takes place which gives off water and binds the CO2 by forming a stable Calcium Carbonate.  When binding to other acidic gases, other calcium or sodium salts are formed.  The Sofnolime offered here contains a color indicator which aids in indicating the useful life of the Sofnolime.  As the sofnolime becomes less effective at binding CO2, the color of the Sofnolime changes to a violet color.  This color change should not be your sole method of determining when to replace your absorbant, but it is an indication of use.

The primary constituents of soda lime include Calcium Hydroxide - Ca(OH)2 (about 70-80%), Water - H2O (about 16 to 20%), Sodium Hydroxide - NaOH (about 1-2%), and Potassium Hydroxide - KOH (about >0-1%).
Water is an important part of the reaction which takes place to bind the CO2 . The general description of the reaction is as follows: First the gaseous CO2 reacts with water to form carbonic acid - H2CO3. Then the NaOH reacts with the carbonic acid to produce Na2CO2 and H2O. The Na2CO2 reacts with the Ca(OH)2 which has been disassociated into Calcium and Hydroxide Ions. (Ca++ and OH-) to produce CaC02 (calcium carbonate, otherwise known as limestone.) The CO2 is now in a relatively stable state. There is a net production of three H2O molecules for every molecule of CO2 which is taken in.

Specific Characteristics

Sofnolime Characteristics 4-8 Mesh 4-12 Mesh
Bulk Density (g/cm3) 0.9 0.9
Moisture Content (%w/w) 182 18 2
Hardness Test (BP 1980) 903 903
CO2 Absorbtion (%w/w CO2)

USP Test (100% CO2)

252% 292%

High Flow Test

(5% CO2 in air/60% RH)

162% 212%


Granule size Distribution


SofnoGranules.gif (11411 bytes)
Smaller granules provide for substantial improvements in absorbtion, but will also slightly increase the work of breathing.   The above graph is provided for guidance and do not constitute product specifications.


Storage of Sofnolime

Sofnlime should be kept sealed and stored in a clean dry environment at an even temperature, preferably between 0 and 35 degrees C (32F and 95F).  Storage at high temperatures can result in a loss of effeciency and a reduced service life due to gradual loss of moisture from the product.  Prolonged storage at sub-zero temperatures should also be avoided.  when stored correctly, unopened containers will maintain absorption capacity for up to 5 years.

You should avoid the following when storing Sofnolime:

Transport of Sofnolime

Sofnolime contains less than 3.5% w/w sodium hydroxide and therefore is NOT classified as corrosive*.  Containers of Sofnolime do not need to be marked with any special hazard warning and they can be shipped by road, sea or air as non-hazordous product.


Personal Protection

Sofnolime is mildly alkaline so appropriate safety procedures should be implemented.   PRotective gloves, goggles, overalls and nuisance dust masks should be worn when working with Sofnolime granules, irrespecitive of whether they are in a fresh or used state.

The granules or any entrained dust should not be allowed to come into prolonged contact with skin and contact with mucous membranes and eyes must be totally avoided.


Exhausted or waste Sofnolime will contain some residual alkalinity, but can normally be disposed of at a suitable land-fill site, etc.

Which mesh size to use?

4-8 grade is the most popular, and is probably adequate for most recreational dives. It is used commonly on Atlantis Rebreathers. (8-12 is not recommended for use with the Atlantis)

The 8-12 will last about 1.3 to 1.5 times longer then 4-8 given the same dives. If you are doing extreme dives you probably want the 8-12, if you are paddling around on reefs, the 4-8 will do just fine.

**Note: Much of the above information was repeoduced from the literature titled "Sofnolime technical data" written by Molecular Products, Ltd., the manufacturers of Sofnolime.


4-8 Grade (This is the larger size)



1-3 Kegs (~44 Lbs/keg) .. 

$no longer available

4-6 Kegs .........................

$not available

7-9 Kegs  ........................

$not available

10+ Kegs  .......................

$not available

8-12    Grade (This is the smaller size)



1-3 Kegs (~44 Lbs/keg) .. 

$not available

4-15 Kegs .........................

$not available

16-31 Kegs  ........................

$not available

Northwood Designs, Inc.
233 Somerville Rd.
Antwerp, NY 13608

ph- 315.287.2877
fx- 315.287.2888


Where to buy Sofnolime...

Copyright Northwood Designs, Inc. All rights reserved.
Revised: September 07, 2005.