I will now try to explain.

This system of classification was developed by a team lead by Dr Steve  Thomas at the SMTL in Bridgend, Walesand is named after him (the Thomas Classification). The main external reference used is a paper by Dr Thomas , Compression bandaging in the treatment of venous leg ulcers, World Wide Wounds.

Headline Classification

There are 3 main classifications or "Types". These describe the correct use for the bandage when applied correctly.

Type 1

Lightweight Conforming-Stretch Bandages.These bandages are primarily for dressing and tube retention. The light weight, highly extensible structure of this group of bandages allows them to conform well to the limb. Ideally the sub-bandage pressure should not alter  significantly in response to changes in tension  or limb circumference and should not be more than a few mmHg at any time.

Examples  Easifix(®S+N)and many others.

Type 2

Light Support Bandages. These are also known as "Short Stretch" or "Minimal Stretch" bandages. They have 2 distinct roles, to give support to joints and the treatment of venous leg ulcers.

These bandages are designed to "lockout" at a low level of extension avoiding high levels of pressure.

Thus they can be used to give support to sprained or strained joints and to prevent swelling without applying high levels of compression to underlying tissues.

The mode of action Type 2 bandages in leg ulceration is fully described on other pages. 

Examples Crepe BP,  Elastocrepe (®S+N) and many others.

Type 3

Compression Bandages. These bandages are all designed to produce a level of compression and are most commonly used to control oedema (especially in venous leg ulceration). It has become necessary to further sub-divide this class by the amount of pressure they produce when properly applied.

Type 3a   Light Compression Bandages

Should produce a pressure of up to 20 mmHg at the ankle on a "normal" leg. They may be used to control early varices for example during pregnancy. They are used extensively as a part of multi-layer compression regimes for the treatment of venous leg ulcers. However they are generally not suitable use alone in treating existing oedema or leg ulcers. On large limbs they are ineffective at producing even low levels of compression. (Laplace's Law)

Examples  Profore#3 (®S+N)and others

Type 3b   Moderate Compression Bandages

Ankle pressures of around 30mmHg. Used for treating or preventing venous leg ulcers. Also used as part of multi-layer compression systems

Examples Co Ban (®3M)Co Fast (®Parema)Co Plus (®S+N)NB. all three were considered borderline with type 3a at one time.

Type 3c  High Compression Bandages

Ankle pressures of the order of 40 mmHg. Indicated for the treatment of venous leg ulcers and gross oedema. May be used in some multi-layer regimes especially for very large limbs.

Examples,  Surepress (®Convatec)Tensopress (®S+N)

Type 3d   Extra-high Performance Compression Bandages

Ankle pressures of the magnitude of 50 mmHg. These bandages are capable of controlling oedema in even the largest of limbs. for extended periods of time. Note that these are very strong bandages, capable of huge amounts of damage. They should only be used where the patient can be regularly monitored.

Example Elastic Web Bandage BP

Summary

There are 3 classes, Type 1, does very little apart from stay in place, very safe. Type 2 supports joints, stops swelling and is safe on most patients. Type 3 produce compression, as a result they can produce damage, the amount and nature of which is dependent on sub class and the patients condition. They should always be applied with caution, following a proper diagnosis and by practiced staff.