▁working ▁face ▁of ▁the ▁su ction ▁cup ▁is ▁made ▁of ▁el astic , ▁flexible ▁material ▁and ▁has ▁a ▁cur ved ▁surface . ▁When ▁the ▁center ▁of ▁the ▁su ction ▁cup ▁is ▁pressed ▁against ▁a ▁flat , ▁non - por ous ▁surface , ▁the ▁volume ▁of ▁the ▁space ▁between ▁the ▁su ction ▁cup ▁and ▁the ▁flat ▁surface ▁is ▁reduced , ▁which ▁causes ▁the ▁air ▁or ▁water ▁between ▁the ▁cup ▁and ▁the ▁surface ▁to ▁be ▁exp elled ▁past ▁the ▁rim ▁of ▁the ▁circular ▁cup . ▁The ▁cav ity ▁which ▁develop s ▁between ▁the ▁cup ▁and ▁the ▁flat ▁surface ▁has ▁little ▁to ▁no ▁air ▁or ▁water ▁in ▁it ▁because ▁most ▁of ▁the ▁fluid ▁has ▁already ▁been ▁forced ▁out ▁of ▁the ▁inside ▁of ▁the ▁cup , ▁causing ▁a ▁lack ▁of ▁pressure . ▁The ▁pressure ▁difference ▁between ▁the ▁atmosphere ▁on ▁the ▁outside ▁of ▁the ▁cup ▁and ▁the ▁low - press ure ▁cav ity ▁on ▁the ▁inside ▁of ▁the ▁cup ▁keeps ▁the ▁cup ▁ad her ed ▁to ▁the ▁surface . ▁ ▁When ▁the ▁user ▁ce ases ▁to ▁apply ▁physical ▁pressure ▁to ▁the ▁outside ▁of ▁the ▁cup , ▁the ▁el astic ▁subst ance ▁of ▁which ▁the ▁cup ▁is ▁made ▁tends ▁to ▁res ume ▁its ▁original , ▁cur ved ▁shape . ▁The ▁length ▁of ▁time ▁for ▁which ▁the ▁su ction ▁effect ▁can ▁be ▁maintained ▁depends ▁mainly ▁on ▁how ▁long ▁it ▁takes ▁for ▁air ▁or ▁water ▁to ▁leak ▁back ▁into ▁the ▁cav ity ▁between ▁the ▁cup ▁and ▁the ▁surface , ▁equal izing ▁the ▁pressure ▁with ▁the ▁surrounding ▁atmosphere . ▁This ▁depends ▁on