There isn’t enough moisture in unpopped kernels to create the pressure, so they fail to burst and open. To make your popcorn pop better, try soaking the kernels in a bowl of water for 10 minutes and then draining them. Then, pop the kernels as usual. The extra moisture added to the kernels helps produce larger and fluffier popcorn.
Another option is to keep the lid ajar if you’re popping your popcorn on the stove. Keeping the lid ajar helps some steam escape from the pot, making the popcorn crispier and fluffier.