holding the air, while a double skin arrangement uses an airtight bladder in a structural casing of strong but porous textile. Single skin construction is simpler, and usually uses RF welding to make the seams. These bladders are usually lighter and dry out more quickly than double skin wings, but if the bladder is punctured, a new bladder is relatively easily fitted to a double skin wing, while repair of the single skin bladder may not be practicable, depending on material and construction details, and the location and extent of the damage. Single skin wings are also easier to decontaminate, particularly if the outer surface is smooth. Single skin wings may use a bellows fold gusset to increase inflatable volume while retaining a relatively compact outline. This can reduce drag while swimming when the bladder is deflated. Cylinder attachment When a backplate is used with a single cylinder, a single tank adapter, or STA, is usually used. The STA is a small metal structure that bolts onto the backplate on the outside of the wings, contains two camstraps, and accommodates the cylinder. Use of a single tank adaptor slightly increases the profile height of the assembly and may affect the centre of gravity which may affect trim. In some cases the increase in height may be undesirable. In some instances, the STA may be omitted, and the camstraps threaded through the wing and backplate. In these cases, the wing will contain a built-in STA in the form of two rods or pads which stabilise the cylinder, or the backplate may be made with a slight channel in the central ridge to hold the single cylinder. Twin cylinders are usually attached to the backplate via bolts, passing through the cylinder bands, and secured by nuts in the central channel of the backplate. An alternative is to use two sets of camstraps and extra slots in the backplate and wing. This arrangement will allow convenient attachment of independent cylinders of almost any size without use of cylinder bands. Some rebreather divers fit backplates to their rebreathers. The exact method of attachment varies between users and rebreather models, and may include modification to the rebreather or using a customised backplate. Some rebreathers are designed specifically for use with backplates. Ancillary equipment The backplate and wing is a minimalistic system, however it does facilitate addition of other equipment. Ancillary equipment, commonly attached to the