Drew,
Booster pads, also called “doublers” or “stuffers,” are absorbent pads that are added inside a diaper to increase the diaper’s overall total absorption. The pads may be rectangular in form or contoured in an hourglass shape to be narrower in the crotch. The pads are placed inside the disposable diaper on top of the diaper’s own absorbent mat, between the leak guards. The booster pad usually sticks to the diaper’s mat by means of an adhesive. The booster pad is not waterproof so, once it has become saturated with urine, it passes additional liquid through to the diaper’s regular absorbent mat. Do note that booster pads are not the same as incontinence pads (which are inserted into the user’s own underwear).
Booster pads markedly increase the time between diaper changes and can save money by requiring fewer changes in a day. Some users change just the pads when they are saturated, extending the length of use of the diaper itself significantly. This works with pads that do not have an adhesive and is easier for those wearing pullup diapers.
For best efficiency, men should position a booster pad higher in the front of the diaper than women.
Some doublers absorb a considerable amount of urine, as much as some diapers. Most booster pads come in sizes, rated for absorbency, such as 12 oz., 16 oz., and even 32 oz.! Booster pads cost much less than diapers and their use can markedly lower the price per ounce for incontinence protection. A booster pad can really improve the absorbency of a less expensive diaper. However, a better quality diaper may be a better and less expensive choice than using a less expensive diaper plus a large booster.
Drew, experiment first with small booster pads. They cost less and their added absorbency should be 100% used.
I do not know UK suppliers, but take a look at this supplier in the U.S.
http://www.northshorecare.com/boosters1.html--John