Due to environmental concerns the use of wood materials is becoming more extensive
and is causing wood supply shortage, therefore the use of Populus genus wood species with a
short rotation period is vital. Populus genus species wood has several shortcomings - it is not
durable, has low density and is hygroscopic. Thermal modification is a technology that can be
used to improve the situation. In this study aspen (Populus tremula L.) was thermally treated
using the Wood Treatment Technology (WTT) device for 50 min at 160 °C (50–160 WTT) and
poplar (Populus x canadensis Moench) was vacuum-treated (VT) 120 min at 204 °C
(120–204 VT), 120 min/ 214 °C (120–214 VT), 180 min 217 °C (180–217 VT) and 30 min
218 °C (30–218 VT). Mass loss (ML), colour change, density, tensile strength along the fibres,
moisture exclusion efficiency and weight loss (WL) after brown rot fungus Coniophora puteana
were determined and also light microscopy images were taken. Aspen veneers showed a ML of
5.3% between 120–214 VT (6.2%) and 30–218 VT (4.6%) treatment that coincided with the same
mass loss in aspen boards cited in the literature. The highest ML was 8.7% calculated from
180–217 VT, while the lowest ML was 2.9% computed from 120–204 VT. The total colour
change ΔE was 44, where lightness parameter L provided the greatest impact that was reduced
twice after modification. Tensile strength reduced by 47% in the WTT process and had ~29%
reduction in the VT process. The WL after fungus C. puteana was 33% at 50–160 WTT. After
VT treatment, WL was 0–2.4%. 120–214 VT and 180–217 VT poplar veneers were the most
suitable for plywood production