Concept:
Linear expansion is given by:
\[
\Delta L = \alpha L \Delta T
\]
Percentage increase:
\[
\frac{\Delta L}{L} \times 100 = \alpha \Delta T \times 100
\]
Step 1: Identify given quantities.
\[
\alpha = 10^{-5}\,\text{K}^{-1}, \quad \Delta T = 100^\circ C
\]
Step 2: Substitute into formula.
\[
\frac{\Delta L}{L} = 10^{-5} \times 100 = 10^{-3}
\]
Step 3: Convert into percentage.
\[
10^{-3} \times 100 = 0.1%
\]
Step 4: Conclusion.
\[
\boxed{0.1%}
\]