The types of forms you can create using these methods can quickly create the desired figure, but they are not meant to be permanent nor are they meant to be replacements for more professionally built forms. Breast forms are often only as good as the bra that contains them. Homemade breast forms often do not hold a particular shape well - their shape usually comes from the bra that contains them. A bra should be substantial and give enough coverage so that the desired contours can be created. Push up bras, see-through lace, and sheer nylon do not work very well in such situations.
Underwired bras provide less movement but provide better shape.
Breast forms usually do not lend themselves to wearing see through garments or producing decolletage - and this can be especially true of homemade forms. Clothing that covers the bra and chest area completely such as garments with high necks, longer sleeves, and sweaters can help hide many flaws in the construction of a homemade form. Some methods for creating homemade forms listed use liquids or gelatinous substances. The handling and maintaining of liquids has some inherent difficulties not to mention the possible danger of puncture in an awkward situation. The use of nylon stockings as an outer breast form surface is common in the methods listed.