Fusion extensions come in 2 types – U-tipped and I-tipped fusion extensions. While U-tipped fusion extensions make use of heat treatment for attachment to the natural hair, the I-tipped fusion extensions are attached through cold fusion. Normally, the use of heat to melt the keratin results in a much more even distribution of the glue and, consequently, longer lasting and more stable hair extensions. This makes U-tipped fusion extensions more desirable. However, for those whose hair are weak and brittle, and cannot withstand even a little amount of heat treatment, I-tipped extensions are an alternate option. The latter is preferred for clients whose natural hair is coarse or curly, since this type of hair is more readily damaged by even the slightest amount of heat treatment. However, for thin hair, U-tipped extensions are more preferable since the weight of the extensions should be evenly distributed, because the natural hair may not be able to sustain concentrated weight at any one point, and may break. U-tipped extensions are also preferred for silky hair to avoid slippage due to concentration of too many hair strands at a single place.