you need some chicken wire a 4 inch to 3 inch reducer 4 hose clamps a couple of zap straps and 2 nylons like your mom uses lol. and a 4 inch and 3 inch end cap. you wrap about a 10 inch piece of chiken wire around the 3 inch end of the reducer and around the 3 inch end cap and you use your hose clamps to hold it on to your reducer and end cap, then you put a nylon stocking over the chicken wire and fasten it with a zap strap, you then wrap another piece of chicken wire around the 4 inch part of the reducer and just make sure it goes past the 3 inch end cap and put the other nylon stocking over the chicken wire now all you have to do is fill in between the to nylon stockings with the charcoal from the pet store and put your other end cap on and clamp it. you can use what ever size reducers to change the size of your filter it depends on what size of dryer ducting you are using. I hope this will help you and anyone who needs to make there own carbon filter. the chicken wire i refer to is the fence type chicken wire in case you didnt understand.