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why do you need insulated trousers??
Probably find something here
https://www.ultralightoutdoorgear.co.uk/mens-clothing-c1/mens-trekking-outdoor-pants-c69/all-trekking-pants-c210 -
here's the good shit:
As Tucas Sestrals trousers
PHD down trousers
Montbell Thermawrap trousers -
Synthetic insulated: Montane Prism, PHD Sigma Primaloft pants
Both relatively light but neither pack small.
If you want super light and don't need insulation, something like Patagonia houdini pants are windproof, sub 100g and pack super tiny.
OMM Kamleika is another popular option, assume pack size is relatively small
I love my Rab Xenon hoodie, had it for couple of years and still going strong. Is there something like that for trousers?