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Custom Fit Seat Inserts

Custom Fit Seat Inserts

Choosing and Using a Custom Seat Insert

By John B. Haydon

A close fit between the driver and the car is important to driver comfort and control, and can even increase a driver's safety in the event of an impact. Pegasus Auto Racing Supplies offers two types of custom-fit seat inserts: the Two-Part Foam Seat Kit and Creafoam Bead Seat Kits.

Two-Part Foam Kit

The Two-Part Foam Kit (Part No. 3385) is the less expensive option, but its use requires at least two helpers, and it can be very messy. This two-part foam can also be used for light-weight support for fiberglass body panels. To pour a two-part foam seat insert, you will need:

  • 1 five-gallon bucket (clean and dry inside)*
  • 2 measuring cups (paper cups, or plastic half-liter bottles with the tops cut off)*
  • Wire coat hanger*
  • Many plastic garbage bags*
  • Newspaper*
  • Tape (masking or cheap electrical tape preferred)*
  • Driver
  • Two or more helpers

* Everything must be disposable except the driver, car, and helpers.

The helpers should wear old clothes they do not plan to wear again. The driver can either wear old clothes, or he can wear his driver's suit if it is securely and completely covered with garbage bags. The driver should also consider wearing an old hat. All long hair should be tied up or tucked out of harm's way. The foam will not come out of fabric or hair, and it stays on your skin for several days.

Begin by lining the inside of the car with plastic garbage bags. The object is to prevent any spilled foam (and it will spill) from getting on any surface of the car (it will not come off easily). Tape the garbage bags in place, but leave a little slack so they do not tear when the driver climbs in. Spread newspaper on the floor around the car and under your mixing area. If the driver is wearing his driver's suit, cover the suit as completely as possible with a layer of garbage bags.

Determine where the driver needs the most support: behind the back, around the ribcage, or under the seat. Loosely tape one garbage bag in the area where support is needed. Tape it with plenty of slack, because the foam will pull the bag as it expands. Do not tape it too securely, because you want the tape to let go before the bag does. Have the driver get in the car.

Now pour some of Part A into one measuring cup and an equal amount of Part B into the other cup. Remember that the foam will expand a lot; do not try to fill the bag with liquid! A second pour can be added later to build up the seat if it is not large enough. This is much easier than trying to clean up several cubic feet of extra foam.

Keep in mind that the closer the mixture is to 1:1 A:B, the stronger the seat will be. Pour the two parts into the bucket and mix with the wire hanger bent into an appropriate shape. The two parts will begin life looking like maple syrup and maple syrup "lite," but the mixture will resemble pancake batter in about one minute. When it does, it is starting to foam and is ready to pour. Do not delay the pour for too long; the mixture pours less well the more it foams.

Now have one or two helpers hold the bag open while another helper pours the mixture, hopefully into the bag and not on the other helpers. The driver can assist by keeping his weight off of the bag and squishing the foam into place where he needs it. Once the foam is in the bag, the driver can begin to settle back into the seat, gradually resting his weight on the foam as it sets up and expands around him. The foam gives off a little heat as it sets up, so sit back and enjoy the feeling!

The foam will be done expanding about five minutes after it starts. About fifteen minutes later, the foam will be hard enough that the driver can get out (avoid stepping on the insert) and the foam will hold its shape. Allow a few more hours before removing the insert from the car, peeling the bag off, and trimming as needed.

Creafoam Bead Seat Kits

The Creafoam bead seat kits (Part No. 4525) require considerably less car and driver preparation, but the real work is in selecting the correct size. The kits are available in six sizes: Kart (5 gallon), Xtra Small (5 gallon), Small (10 gallon), Medium (15 gallon), Large (25 gallon), and Xtra Large (30 gallon). It is generally better to err on the larger size, since excess beads can be dumped out before use, and a bag that is too large can be trimmed after the seat is done. You can't add material later with these kits. The only tools required are a magic marker and a shop vac or vacuum cleaner with a hose.

To choose a kit size, first determine how much support is needed, and where. If the driver only needs a small backrest, the Kart or Xtra Small kit should suffice. If the driver needs lateral support from the torso down to the thighs, you may want to get the Medium kit. If the driver needs to be moved forward and up as well as supported laterally, you may need the Xtra Large kit.

Instruction Summary:

These instructions are just a quick summary of the detailed instructions included with the Creafoam seat kits. Expect to spend about two hours fitting the seat and 8 hours letting it cure.

First lay the bag in the car to check its size. If it is clearly too long or too wide, simply pull the beads from one end or the side and fold the bag over to take up the excess. Do NOT cut the bag! If the size is close but the volume of beads is too great, dump some of the beads out of the bag. Don't let them get away; you will never catch them all. Do not worry if the bag is only a little too large, as excess will be trimmed from the seat when it is done.

Next have the driver sit in the car on the bag and adjust the position of the beads until he is supported comfortably. Use the vacuum cleaner to suck some air out of the bag so it will hold this shape. Have the driver get out of the car and mark with the magic marker where the thick spots and thin spots are on the seat. You want to be able to re-create this pattern of support without much trouble. Remove the bag from the car and spread it out on the floor.

Now mix the two-part resin included in the Creafoam seat kit according to the kit directions. Pour the mixture into the bag and knead it so that it gets distributed to all the beads in every corner of the bag. You want every bead covered in resin as completely as possible, with no pockets of excess resin. Once the resin is thoroughly mixed with the beads, put the bag back in the car and redistribute the beads away from the thin spots and into the thick spots. Have the driver get in the car and sit on the bag, squishing the beads around as needed to get maximum support and comfort. Use the vacuum cleaner to draw all of the air out of the bag as the driver rests his full weight on the bag. The bag will now hold its shape. Remove the driver from the car and let the resin cure overnight.

After the resin has cured, peel the bag away from the foam and trim the insert as needed. You now have a seat insert which is very similar in construction to the impact-absorbing liner in your helmet.

Covering your seat

With either seat, you have a few options for covering. The most basic is to wrap it with gaffer's tape or racer's tape (the Creafoam kits each include a roll of gaffer's tape). The drawback to this method is that if the tape shifts, the exposed adhesive residue can get on your driver's suit. This can be minimized by using gaffer's tape instead of racer's tape and wrapping the tape vertically rather than horizontally, but it cannot be completely eliminated.

A more elegant solution is to use 3M (or similar) spray adhesive to attach a fabric covering to the seat insert. We recommend Nomex or other fire-retardant material. Cotton is naturally flame retardant, so it would be a good choice. You could use a favorite old cotton t-shirt or sweatshirt, an old driver's suit that no longer fits, or visit the fabric store for something that matches your car.

Quick comparison

Two-part foam: Lots of prep work, but cheap and cures quickly. Better choice for one-time drives and rentals.

Creafoam: Higher price, overnight cure time, but much less prep work and fewer tools needed. Not an economical choice if the seat insert will only be used once or twice.

Two-Part Foam Seat Kit
Creafoam Bead Seat Kits
Custom Seat Insert Kits & Padding

This article was first published on 12/4/2008.

It was most recently modified on 3/26/2015.