This has been an ongoing problem. I love white pants, but I cannot for the life of me find pants that are not see through. I ordered a pair of Canali pants last summer (twill cotton) hoping they would not be see through. For $450 I thought they'd be fully lined. No such luck. Same thing this season with Armani, Loro Piani and Paul & Shark.
I had hoped that the Howard Yount winter white weight pants (15.9 ounces) would work, but I didn't want to take the chance since they were unlined.
I know Trini has a pair of PRL white flannels that appear to avoid this problem. But they were from a few seasons ago. Other than ordering custom off-white flannels I've never seen anything similar for sale.
My tailor can make up white flannels fully lined for me for about $350 - but I'd need two pairs - one for summer and one for winter. Not sure if I can sneak that pass the Mrs
The Mrs cannot understand why men's white pants are not lined when most women's white pants are fully lined.
Currently I rely on my white 501s, but those don't work for work.
If anyone finds a maker who offers fully lined, please let me know. I'll buy 5 pairs to see me through the next decade.