Earlier this week, the NFL announced a new stadium bag policy, changing the rules about what is and isn't allowed into league facilities. To make that long story short: bigger bags are no longer permitted, but small clutches are, and clear bags (either brought from home or purchased at the stadium) will be allowed. You can read the full policy here.
What hasn't been discussed as widely is that part of the new policy prohibits fans from taking seat cushions into stadiums. The league outlined the reasoning for that decision in a FAQ item posted at the link above.
Are seat cushions allowed to be carried into the stadium?
No, they are not due to the large size and because the way seat cushions are constructed would allow them to be used to conceal a potential explosive device.
Buffalo Bills fans have been bringing seat cushions to Ralph Wilson Stadium for years - particularly those fans seated in the upper deck, where bleacher-style seats are still present. Those fans will no longer be allowed to bring those items into the stadium this year - and if they're still looking for seat cushioning, they'll likely need to resort to blankets, which are still permitted in NFL facilities.