Vivica Fox Hair Collection - SMART Weft (SMWYK) - Extensions/Weaving S - Super Thin, M- Maintains Shape, A - Airy, R- Re-Useable, T - Tightly Sealed. Vivica's SMART Weft is revolutionizing traditional weft. It is the flattest weft available on the market. Lump free, Odor free, Tangle free and Shed. SMART Weft is not a weave, just like your own hair.