[Question] How has the cost of clothing insulation changed since 1970 in the USA?

I some­times hear the claim that in­no­va­tion in the phys­i­cal world has stag­nated since around 1970. More speci­fi­cally, chap­ter 1 of The Rise and Fall of Amer­i­can Growth by Robert J Gor­don claims that there has been ba­si­cally no in­no­va­tion in cloth­ing other than changes in fash­ion. This is some­what con­trary to my in­tu­ition (al­though I definitely be­lieve that in­no­va­tion in the 50 years be­fore 1970 was greater that in the 50 years af­ter), and price of in­su­la­tion seems like a rel­a­tively ob­jec­tive met­ric for this.

My favourite type of re­sponse would be time se­ries data of clo per in­fla­tion-ad­justed dol­lar, but I’d also ap­pre­ci­ate peo­ple’s sub­jec­tive ex­pe­rience of this.