When there's a long-term supply arrangement in place, it often contains a fixed price for a certain period of time, with a chance to revisit this in the future. For a short-term arrangement, they've signed up for a specific price, which was the going rate at the time. For most arrangements, to be frank, there's a fixed price in the contract, but for the really long-term ones there is some variation possible, up or down.
The member is quite right that for things like face shields, things are quite stable, so there is an easier story going forward. There are other commodities that are still pretty tricky. Gloves are one that's really worth keeping an eye on. That commodity's price might go up. The price there is quite volatile, I'd say.