Wood is a natural product, it cannot be compared to an inert material such as UPVC or another man made substance. As a natural product, it will be affected by its own growth conditions and subsequent levels of moisture that it holds.
Some customers might be surprised to hear that factories do not produce wall logs that resemble a banana or propeller with intended machining.
All components are manufactured perfectly true, no twists or bending. However, wood being wood can decide to react to the machining process – varying moisture content along a logs length and or non slow grown timber can result in a perfectly true log bending and twisting.
Any manufacturer that will guarantee ALL its wall logs arriving with the end user as straight as when they were machined is on a sticky wicket ! Are twisted boards a problem ? No, not really, they just need to be used in a more considered way.......