I got one of the laptop soft cases below from Amazon to see if they'd work as a pannier inner bag. Haven’t used it in anger yet, but I did stuff it with 30 t-shirts and 2 pairs of jeans to see how it'd fit in a Touratech 45l Zega Pro pannier. Seems to be decent quality. Gonna get another for the other pannier.
https://www.amazon.co.uk/dp/B07D5QG...olid=1HVYKDRNS9JFW&psc=1&ref_=lv_ov_lig_dp_it
https://www.amazon.co.uk/dp/B07D5QG...olid=1HVYKDRNS9JFW&psc=1&ref_=lv_ov_lig_dp_it