Lub hnab U-shaped yog tsim los ntawm peb lub cev vaj huam sib luag, ib qho uas npog tag nrho ntev ntawm lub hnab, ua rau hauv qab thiab sab, thiab lwm ob daim ntaub sewn rau hauv daim loj dua los ua rau lwm sab. Zoo ib yam li lwm hom kev tsim kho, U-shaped hnab yog square tom qab sau, tshwj xeeb tshaj yog U-shaped hnab nrog stretch tuav. Lub hnab U-shaped yog cov qauv kev lag luam thiab yog hom nrov tshaj plaws, muab kev nyab xeeb ua haujlwm siab (SWL) thiab ruaj khov.
Round hnab yog ua los ntawm tubular ntaub uas ua rau txhua sab ntawm lub hnab, cia tsuas yog sab saum toj thiab hauv qab ntawm lub hnab yuav tsum stitched. Txawm hais tias cov ntaub yog tubular, lub hnab puag ncig yuav tseem zoo li lub hnab square thaum ntim. Muaj ib qho kev xav tsis zoo txog kev sau cov duab ntawm lub hnab puag ncig, lawv tsis yog cov lus puag ncig, lawv tsuas yog tsim los ntawm ib daim ntaub uas ua rau tag nrho plaub sab ntawm lub hnab.
Lub 4-daim FIBC yog tsim los nrog plaub tus neeg sewn ua ke los tsim cov qauv square. Thaum ua tiav, 4- lub hnab ntim khoom yuav tuav nws cov duab plaub. Feem ntau, plaub-thooj hnab tuav zoo dua li U-zoo li lub hnab, uas tuav cov duab zoo dua li lub hnab puag ncig. Qhov tsis zoo tshaj plaws ntawm 4-daim Fib Cs yog tias lawv xav tau ntau txoj hlua. Txawm li cas los xij, 4-daim Fib Cs yog qhov zoo tagnrho rau kev khaws cia vim lawv khaws lawv cov duab zoo dua thaum sau.