How to Crisp Stale Crackers & Chips: Livestrong.com.
The staling of dry, crisp foods such as crackers, tortilla chips, and cookies occurs because the atmosphere gets absorbed by the item's starches, which makes it softer and robs it of its crisp texture.
This process can be reversed.If you keep the recrisped items dry, they will stay crisp.
Place larger items such as cookies and graham crackers on a wire rack set in a baking sheet if you want to avoid overlap.Place the sheet on the middle rack of a 225-degree oven for 15 to 25 minutes, until the food is crisp again, stirring (or flipping, in the case of cookies) halfway through baking.