Pantyman said:
It doesn't have to be. The leak guards are what suppose to keep everything in. I know I like mine to so I get a nice brief type look. But soon diapers just have loose leg opening
It does have to be. Leak guards were not designed to be waterproof. If they were they would be made of non permeable plastics like backsheets are. Instead they are made of the same non woven plastics as the topsheet. They are intended to hold solids and help direct the flow of fluids up the diaper.
Here is an excerpt from patent #EP1933798B1 issued in 1998 currently held by P&G with a link for reference. It's in reference to the figure below.
Containment is achieved because the surface material would have to flow up the channel 96, which direction is substantially directly against the force of gravity when the wearer is in an upright position, in order to penetrate and flow over the distal edges 66 of the barrier cuffs 62. However, should such material flow beyond the barrier cuffs 62, it is retarded from leaking out of the diaper 20 by the gasketing effect achieved by the gasketing cuffs 56, as they draw and gather the side flaps 58 about the legs of the wearer, thereby providing a second and independent effective barrier against leakage.
And this excerpt id from patent #US4695278A issued in 1985 and currently held by P&G. This is most likely their inception in design.
The major function of absorbent articles such as disposable diapers and adult incontinent briefs, is to absorb and contain body exudates. Such articles are also intended to prevent body exudates from soiling, wetting, or otherwise contaminating clothing or other articles, such as bedding, that come in contact with the wearer. The most common mode of failure for such products occurs when body exudates leak out of the gaps between the article and the wearer's leg or waist to adjacent clothing because they are not immediately absorbed within the article. This is most evident with loose fecal material which is not easily absorbed by the absorbent article and tends to "float" on the top surface of the absorbent article.
If leak guards were designed to hold fluids then baby diapers would already have loose leg openings. Baby diapers are miles ahead of adult diapers in construction and design and would have reflected this design already.