<p>Experimental investigations of corrugated cardboard tubes under various boundary restrictions (one-sided restriction and two-sided restriction) were conducted to better understand the characteristics of the vertical upward flame spread in hollow combustible materials subject to boundary restrictions. Different thicknesses (expressed as <i>δ</i>, from 1 to 8&#xa0;mm) and different inner diameters (<i>d</i>, from 30 to 80 mm) were also considered in this experiment. Through comprehensive analysis of key flame spread parameters, the study elucidated the effect of boundary restrictions on flame spread dynamics in hollow structural combustibles. The obtained findings show that under one-sided restriction, both mass loss rates along with flame spread rates are higher than those under two-sided restriction. While the values of jet flame height under one-sided restriction are smaller than those under two-sided restriction. The study find that the flame spread in hollow combustible materials is more significantly influenced by the sample’s inner diameter than by its thickness or the presence of boundary restrictions. The conclusions of the study have effective implications for fire safety design in construction.</p>