Let
$F$ be a non-separable
$\text{LF}$-space homeomorphic to the direct sum
${{\sum }_{n\in \text{N}}}\,{{\ell }_{2}}\left( {{\tau }_{n}} \right)$, where
${{\aleph }_{0}}<{{\tau }_{1}}<{{\tau }_{2}}<\cdot \cdot \cdot $. It is proved that every open subset
$U$ of
$F$ is homeomorphic to the product
$\left| K \right|\,\times \,F$ for some locally finite-dimensional simplicial complex
$K$ such that every vertex
$v\,\in \,{{K}^{\left( 0 \right)}}$ has the star
$\text{St}\left( v,\,K \right)$ with card
$\text{St}{{\left( v,K \right)}^{\left( 0 \right)}}<\tau =\sup {{\tau }_{n}}$ (and card
${{K}^{\left( 0 \right)}}\le \tau $), and, conversely, if
$K$ is such a simplicial complex, then the product
$\left| K \right|\,\times \,F$ can be embedded in
$F$ as an open set, where
$\left| K \right|$ is the polyhedron of
$K$ with the metric topology.