Saturday, January 26, 2013

Under-thrusting diaphragms

A latex All-Flex arcing spring diaphragm was best for under-thrusting

Under-thrusting play: On another forum there was a recent discussion of a method of under-thrusting that involves using a diaphragm that is a size too large. I suppose in some limited circumstances that might be possible. However, for the maximum comfort of both parties I think for under-thrusting play a diaphragm at least one size (5mm) smaller than the size a woman needs for contraception should be used. The Ideal style diaphragm for under-thrusting play was the latex Ortho All-Flex arcing spring. However, Ortho switched from latex to silicone for its All-Flex in the fall of 2008 and stopped making the coil spring rim style entirely so the few of us who still have a latex All-Flex in good condition are fortunate indeed. The 70mm latex All-Flex shown in the photo accompanying this post is two sizes too small for me and is the size I use for under-thrust play. As I’ve mentioned before a latex dome is stretchier and has much better heat transfer properties so it’s much more fun to use than the newer silicone All-Flex. And for those fond of the rubbery/fishy scent of a diaphragm that has marinated in vaginal and cervical fluids during a lengthy insertion (more than 24 hours) a latex dome has a much stronger odor than does silicone. The scent of old semen discharge adds to the stench which some vaginal fetishists find intoxicating.

An under-thrust study: A few years ago I participated in an under-thrusting study while wearing correctly sized [rather than a size or two smaller] and properly positioned diaphragms of all the available rim styles – Arcing, coil and flat spring with both uncut partners of very large girth and more normally equipped men. With the latex All-Flex (the easiest rim style to under-thrust) for the large girth men it was uncomfortable for both of us. Those encounters were part of a study my women’s clinic conducted to see which rim style put the wearer at the greatest risk of having her diaphragm accidentally under-thrust while using it for contraception during vanilla sex. All the women participating in the trial had deep post-pubic vaults as most women do. women with shallow or no post-pubic vaults aren’t good candidates for effective diaphragm use because the anterior rim is positioned where it may hurt a partner during vanilla sex and is easier to under-thrust than if the woman had a pronounced/deep post-pubic vault.

The results of the study showed that the easiest to under-thrust was All-Flex (arcing), then Milex Omniflex (coil) and Semina (coil) of similar ease. Then Milex Arcing and the most difficult was Reflexions flat spring. The Milex Arcing is more difficult than the All-Flex because it folds with two elbow hinges so the rim has to be positioned exactly right for a thrusting penis to cause it to fold. The switch from latex to silicone has not changed the study results. Of course no diaphragm is risk free since acute angle brute force thrusting can stretch the vaginal wall to allow a penis under the rim even of a Reflexions flat spring.

Penetration depth: In missionary penetration depth can depend on the shape of the couple’s pubic bones making standard missionary unlikely to attain deep thrusting unless the male partner is very well endowed. During the trial when I was taken in missionary all of my uncut partners of very large girth came away from their encounters with sore or sometimes raw frenulums. One was in so much pain he lost focus and couldn’t finish. With one or both partners having prominent pubic bones it may be necessary for the woman to put her legs on her partner’s shoulders to give him the depth to reach her cervix and the thrust angle needed for under-thrusting. I have a prominent mons veneris and at that angle I had to use lubricating gel on my labia to prevent perineal tears that less experienced women in the trial were having. It was a tiring and not all that pleasant experience.

Doggie style was somewhat better - wasn't nearly as traumatic for the men, but for me having the rim forced into my posterior fornix when he’s trying to get under it was still uncomfortable. While still tight there was more room between the back of my pubic bone and the rim (because on my elbows and knees my uterus and cervix are pulled deeper into me by gravity) for him to get the smooth top of his glans under it. And of course because of the gravity effect I could take a longer man more comfortably. Doggie is certainly the preferred position with a well endowed partner because his frenulum caresses my G-spot while his tip thrusts into my cervix.

Again the above results were for large girth men with the woman wearing a correctly sized diaphragm. For a man of more normal size the order of ease to under-thrust didn’t change, but the men suffered less physical damage. With a too small diaphragm you get all the pleasures of under-thrusting while lessening the discomfort and possibility of damage to your male partner(s). The only down-side of using a too small D is that for some women it may be difficult to remove afterward.


  1. I do not understand the fascination with underthrusting. But, then, my diaphragm whilst in bed is strictly a fetish at this point and it serves nor real purpose whether I have a penis in me or not. I have, over the years, used all three types - coil, arc and flat spring - and have never been underthrusted. Likely because I never had a partner who found fascination with that.

    Eva has, since I gave her a diaphragm as a present, found a wonderful use for a diaphragm in a post-menopausal woman. She has a very dry vagina and is not on hormones. As a result, she has needed lubrication and, with a diaphragm, has discovered a great delivery system. She fills the dome, really fills, with personal lubricant, she uses Surgilube, before insertion. She finds that this puts plenty in her and with each thrust, the man is squeezing a bit more out from under the diaphragm. Next best thing to lubricating naturally and she has not had to take a break to refresh lube since she began using this.

    I continnue to sleep most nights with a diaphragm inserted. It gives me great comfort, a feeling of security and intensifies my response to both masturbation or Eva's skills. The few times I choose a real penis, I use it and the orgasms are generally improved. Perhaps that is partly the phenom that you describe wherein the lower part of the rim is right at the G-Spot. No man has even commented upon it and Eva simply expects to find it there. I would rather have my period back but this is quite a satisfactory replacement. I have even recommended it to one woman who became nearly non-orgasmic after menopause. Results not reported yet.

    1. I have lovers who seem to need to under-thrust to be in control, to circumvent their partner's barrier protection. Most seem to need to prove their masculinity in that way. One wants to watch me insert my D for him which is a problem for two reasons: By then I'm aroused and tented so even inserting a correctly sized D is difficult and of course the one I use for under-thrusting play is two sizes smaller. I have to squat and push down and still can barely get the rim behind my cervix and I have long fingers. He seems to love watching me struggle to get it positioned correctly knowing he can turn that form of protection against me by filling the dome with molten pearl. He knows that afterward it will pool around my cervix as he sleeps with his head on my chest.

      Thank you for sharing that you find wearing a D gives you a feeling of comfort and security. I feel the same way; more so than with my Oves, though I know for me Oves is much safer for rough and dive-sex except during menses. I've never admitted it before because it seemed childish (swapping a teddy bear for a diaphragm as an adult pacifier) but in thinking about it I'm pleased that we have found a meditative use for such an intimate feminine device in addition to it enhancing a our vaginal orgasms.

      I think having ones G-spot caressed by the rim is a function of pelvic anatomy because while it works for me – especially the stiff rim of Reflexions - I rarely hear of other women having their diaphragm enhance an orgasm and my patients aren’t the least reluctant to discuss that sort of thing with me.



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Powys , Wales, United Kingdom
I'm a classically trained dancer and SAB grad. A Dance Captain and go-to girl overseeing high-roller entertainment for a major casino/resort