Editing Cervical cap (section)

===Rim===
Per Stopes (in the 1920s) they should be made of very pliable soft rubber which should not be wrinkled or withered.

Caps of the 1920s had three types of rims: solid rubber (like an o-ring), air-inflated rubber, or a spring encased in rubber. Stopes recommended the all-rubber cap with the solid rubber rim{{sfn|Stopes|1924|pp=150–1, 156}}  There is also the question as to what is the best shape of the rim cross-section so that the penis is less likely to dislodge the cap by contact with the rim.  Some caps such as the Prorace, advocated by Stopes, had a wide but flat thin rim so that a penis contact would tend to push the rim against the fornix which it is already resting against.<ref>See the diagram in Chalker2, p. 78, of the penis wedging itself between the vagina and the side of the cervix while making contact with the rim.</ref>