Composites 101: An Introduction To Vacuum Bagging

There are numerous ways to fabricate composite parts utilizing carbon fiber and glass fiber. One method is the manual layup, a method that sometimes relies on vacuum bagging to help the materials consolidate more uniformly. Vacuum bagging is a procedure that is utilized both commercially and by DIY fabricators.

We have written this post to introduce our readers to the concept of vacuum bagging, what it does, and how it works. Note that we sell vacuum bagging kits and supplies. In fact, we have everything you need to complete manual layups at home or in your professional shop.

The Point of Vacuum Bagging

It is not absolutely necessary to vacuum bag composite parts. So why do people do it? If you were to create a carbon fiber body panel for a classic car, you would start by creating a mold, or a tool as we call it in the industry. You would then lay carbon fiber fabric on the mold and cover the fabric with epoxy resin. Then another layer of fabric and more resin, continuing until you built it up to the thickness you wanted.

At that point, you could let it cure as-is. But if you wanted to guarantee that air is removed and the resin is equally distributed throughout the fabric, you would turn to vacuum bagging. The process of vacuum bagging is intended to fully consolidate resin and fabric so that the finished product offers consistent strength and integrity throughout.

Vacuum bagging sucks all of the air out of the layup ensuring you create a part with minimal defects. The end result is a more consistent layup that cures into a more uniform part. That is really the long and short of it.

How It’s Done

The nice thing about vacuum bagging is its simplicity. It is as easy to do as it is to understand. Once a layup is complete, you apply a peel ply layer to help remove the finished part later on, followed by a breather layer that allows air to escape while simultaneously absorbing any excess resin. The entire layup is then covered with the vacuum bag and sealed around the edges.

Next, you connect hose and pump. Turning on the pump sucks out all of the air and creates a bit of pressure. From this point, you can leave the layup alone and let it cure in place or put it in an oven. In some commercial settings, the vacuum bag layup is put in an autoclave for curing.

Pros and Cons of Vacuum Bagging

Vacuum bagging offers benefits that make it the right choice for some projects. First and foremost is consistency. You just get more consistent parts this way. Another benefit is quality. If you need a high-quality part for which structural integrity is non-negotiable, combining prepregs and vacuum bagging is the way to go. The fact that the vacuum bag creates pressure on its own eliminates the need for autoclave curing in some cases (but not all) saving money by saving energy.

In terms of the cons, let us talk about pressure again. Autoclave curing relies on a combination of temperature and pressure to consolidate resin and fabric. High performance parts are typically cured in an autoclave. Thus, the advantages of vacuum bagging are diminished. With vacuum bagging, you also generate waste.

Vacuum bagging is a great practice for DIY fabricators. There are plenty of online videos explaining exactly how it’s done. In the meantime, feel free to contact us to order your vacuum bagging supplies. Don’t forget to ask about our fabrics and resin too.