The two latter groups speak mutually intelligible languages and carry on a symbiotic trading partnership, and are most concentrated in the Tawi-Tawi province in the Sulu archipelago. The Badjao and Samal mat, design-wise, is undisputedly the most interesting tradition in the whole country. The most commonly used material is the pandanus plant which grows abundantly in the limestone-based island of Tawi-Tawi. The pandanus grow wild and untended in the shores and sandy beaches. The techniques for preparing the pandan and weaving the mats are generally similar throughout Sulu. In 1962, an American Peace Corps volunteer named David Szanton (since then an anthropologist and currently head of the International Programs at the University of California, Berkeley) made a survey of the area and described the process of mat making:  "First, the thick pandan leaves are cut and center rib are removed. The two halves are separated then rolled in a coil, about one foot in diameter. Tied and held at the bottom of a pot by a rock, the coil is cooked by the boiling water, removing some of the color. The coil is then dried in the sun, opened and the leaves flattened with stick. They are drawn through a small metal bladed tool, which cut each leaf into four or five narrow strips. Edge strips are discarded and other are bundled loosely and left to bleach further in the sun before being resoaked in cold water for about 12 hours. By that time they have been sun-dried and softened with the stick once again, the natural color has almost completely faded and dying can begin." The dyes used are chemical, producing green, orange, red, violet, blue, yellow. After dyeing they are placed in shade to dry and again gently beaten to further soften the material. These preparation usually takes about a week, while the weaving can take from two to five weeks. The mats woven by these two groups could be distinguish from each other by their design and use of colors. The small mats have four general patterns: stripes, multi-coloured squares, chequer of white and other colours, and a zig-zag pattern. The Samal mats are muted in colors and are softer to the touch, which is achieved by repeated beating during the preparatory phase. The slightly glossy effect on the surface is achieved by diluting the dye with some coconut oil. These later techniques in the preparation is not done by the Badjao, making their mats less pliable than that of the Samal and a bit stiff when newly woven.