Namkhaeng sai (Thai: น้ำแข็งไส, pronounced [námkʰɛ̌ŋ sǎj]; lit. 'shaved ice'), also known as wan yen (หวานเย็น [wǎːn jēn]) or chamba (จ้ำบ๊ะ [t͡ɕâmbá]), is a Thai shaved ice or snow cone dessert. It is simply shaved ice in a bowl, poured on top with sweet syrup and condensed milk.

Other desserts such as sarim, thapthim krop, and lot chong are partially similar to namkhaeng sai with different ingredients. Many desserts from other countries like bingsu and kakikori share characteristics with namkhaeng sai.^{[citation needed]}

During the reign of King Rama IV (Mongkut) of Siam, ice was imported, leading to the construction of the first ice factory and consequently enabling the invention of namkhaeng sai. Ice was sent from Singapore, packaged inside a wooden crate, and transported by water on the steamboat named Chao Phrayam. Chao Phraya Phisonsombatboribun (Yim Bisalayaputra), titled Phra Phasisombatboribun, issued the ice order which was considered astonishing at that time.

In 1905, the first ice factory in Thailand was established by Phraya Bhakdi Noraset (Lert Sreshthaputra) at Saphan Lek, Charoen Krung Road. It was named "Siam Ice Factory"; people also called it "Nai Lert Ice Factory" which later on spread to suburbs around Bangkok. Ice was then adapted for use in desserts such as lot chong, Thai cantaloupe cake, sarim, thapthim krop, taro, and namkhaeng sai. First namkhaeng sai originated from the Chinese in Phetchaburi province, combining shaved ice with pathongko and red syrup. Later in 1947, condensed milk was very popular and became one of the ingredients poured on top to flavor namkhaeng sai, which then was called chamba. There are two reasons for its name, first is that namkhaeng sai's shape is similar to women's bosom and apparel color of chamba erotic dancer. The other reason is the distortion of the Teochew Chinese word chamba for its vague pronunciation.

Nowadays, chamba is modified to have diverse ingredients and make it more savory and valuable. Many restaurants use bread in namkhaeng sai but some may use cheesecakes or brownies. Additionally, not only has red syrup been used but also juice, tea, coffee, chocolate powder, or milk. Decorated with toppings such as fresh fruits, candied fruits, grain, jelly, crackers, cereal, and others according to each restaurant's idea. The dessert can easily be found in shopping malls, local markets, or street stalls. It is still one of the most popular cool-down desserts for everyone to date.

Namkhaeng sai is by its meaning just ice getting shaved off by shaved ice machine or shaved ice table becoming ice flakes and piled up to make the shape of an ice mountain. This is the main part of the dessert namkhaeng sai. Next is putting the ice flakes into a container, usually a bowl or a cup in some shops, to prepare it for dressing with syrup and toppings. We then pour the syrup of choice on it to create different main flavors, some examples of these syrups are red syrup and condensed milk. The product we have right now is essentially a completed simplest form of namkhaeng sai and is ready to eat. However, to give it more textures and add variety to one’s preferences, nowadays shops always have choices for toppings to choose from; cereal, bread, and sticky rice are such toppings. After adding these to the bowl it is now ready to eat.

The namkhaeng sai mentioned above is sold at street stalls or small shops. In restaurants, namkhaeng sai may have its preset ingredients which come on different menus. Some of them also became signature dishes or portray the shop’s intentions and motivations.

Namkhaeng sai aside from signature menus in restaurants don't have a specific set of ingredients and is usually selectable from the things available at the time of ordering. Customers can choose several ingredients, excluding syrups and condensed milk, up to 4-5 to put in their namkhaeng sai bowl. The ingredients commonly found to be used in namkhaeng sai are listed below.