What can you do before benjamin franklin overland park arrives? For bigger gaps like a chimney flue you will need specialist products a chimney balloon simply inflates and blocks the chimney flue preventing cold air from rushing in, and hot air rushing out. The coke/pepsi idea is fantastic! i don't like either anyway, and it makes a lot of sense to use great hub and very useful as many have this problem at one time or another voted up! Concrete, cement or builders’ rubble in bedford.