A number of motorcycle pants are not standard equipped with all possible membranes and liners available. On the one hand because they already REACH a high level of quality and usability without them, on the other hand, because many thermal liners remain unused throughout most of the year. Too hot in summer, you don't ride in winter.
If you want a thermal lining for a pair of pants which do not have one by default, you have come to the right place.
These are specific products, using proprietary technology. Not universally applicable.