Sbai (Khmer: ស្បៃ [sɓaj]; Lao: ສະໄບ [sā.bàj]; Malay: Sebai; Jawi: سباي; Thai: สไบ, RTGS: sabai [sā.bāj]) or phaa biang (Lao: ຜ້າບ່ຽງ [pʰȁː bīaŋ]; Thai: ผ้าเบี่ยง [pʰâː bìaŋ]) is a shawl-like garment worn by women in Cambodia, Laos, and Thailand to cover the breasts, while in Sumatra, Borneo and the Malay Peninsula, the same term is used to describe a cloth hanging from the shoulders. The sbai was derived from the Indian sari, the end of which is worn over one shoulder.

The term sbai is the contracted form of vowels which has its ultimately original roots from the Austronesian term *cahebay, which was diversified as the first exodus in Taiwan as the Formosan term *sapay from south China between 5,000–4,500 BCE, and the second exodus to the Philippines, Indonesia, and others occurred around 3,000–2,000 BCE.

Its vowel sequence was contracted from south China to the first exodus: *cahebay→*cahbay→*cahpay→*sapay (meaning: 'to hang'). According to the Proto-Austronesian Phonology of Cornell University Southeast Asia Program (SEAP), there is the diversity of the term *cahebay or *sapay into subgroups of other languages families as follows:

Sbai is derived from the Indian sari, which may have been introduced to Southeast Asia through the Indianized Kingdoms, the most notable being Funan, Srivijaya, and the Khmer Empire, which spread clothing and other traditions and elements of Indian culture.

There are multiple texts and stories in Khmer culture concerning the history of sbai, which was likely introduced during the Funan era from India alongside Sompot Chong Kben in the first century AD, making it one of the earliest major civilizations to use their own version of the sbai. The sbai is mentioned in the legends of Preah Thong and Neang Neak. In one scene, Preah Thong clings to a piece of cloth worn on the Nagini in order to make the journey to the Nāga's kingdom; that piece of cloth is a sbai. In that tale, the sbai is symbolic of the tail of Neang Neak, the Nāga princess.

In the Angkorian period, although it was common for men and women to be topless; however, clothes for the upper body were worn: the bas-reliefs of Bayon, Preah Khan, and other Angkorian temples depict women wearing a shawl-like sbai while religious male figures are adorned with stylized sbai. At Angkor Wat, there are depictions of topless Apsaras holding sbai connected to their sampot, while the northern wall of Angkor Wat depicts a group of ladies wearing long sbai holding various offerings.

Nowadays, sbai, along with chang kben and sampot, are regarded as Cambodia's national costumes. Sbai most often used in traditional Khmer weddings with different type and decoration during the rite of Preah Thong Taong Sbai Neang Neak (transl. Preah Thong holding on to the sbai of Neang Neak) which represents the legend of the foundation of Funan and where the groom holds on to the bride's sbai as they go to their room. The groom also wears a sbai.

For men, especially Brahmin and Buddhist monk, the sbai called sbong sbai trai chivor, and is considered the robe of Hindu and Buddhist monks. For women, sbai can be freely used and in different ways such as to wrapping it around the body, covering the shoulder, and commonly covering the breast and stomach over the left shoulder. Different styles of sbai are used by Cambodian women based on their preferences and traditions.