Measure the wall, door and ceiling size in square feet. You need to know how much egg crate foam to order or purchase. It is always smart to order more than you need.
Order or purchase the egg crate foam. There are several locations on the Internet that sell the product. If there is a store close to you, it is better to purchase it in person because it is going to save you money on shipping.
Cut the egg crate foam with sharp scissors. Make sure the sections you cut are long enough to stretch from the bottom of the floor to the ceiling.
Apply either double-sided tape or Velcro to the flat-end side of the egg crate foam. Apply the material to all four sides.
Apply the reverse side of the Velcro onto the wall if you are using Velcro to attach the foam to the wall. Although Velcro is more expensive than double-sided tape, it does allow for easier removal. If you don't care about the aesthetic look of the egg crate foam, you can use a staple gun and staple the egg crate foam to the wall and ceiling.
Install the egg crate foam around the corners of the wall first. Cure the egg crate foam so it creates a rounded corner instead of a sharp angle. You want the egg crate side of the foam to face the room.
Add the foam to the remainder of the walls and door. Make sure to measure the size of the door so you can create a foam cut-out of the exact size.
Attach the egg crate foam to the ceiling. (You may need a ladder for this job.) It is important to cover the ceiling because sound waves are going to bounce off of it if it isn't covered.