Bumper fabric & How to Make Your own Bumper Numbers

Bumper fabric - as a long-time seamstress and sailor, and now a FIRST Mentor, here’s everything you need to know about bumper fabric (for the non-sewer FIRST team member).

What has been recommended: “duck cloth” and Cordura (which is a name brand)
Problem: you’ll see descriptions including denier, weight in ounces or grams, and cotton/acrylic/nylon/polyester/blends. If you don’t sew or make sails, this means NOTHING. to you. “Cordura” is a name brand, so it’s even more confusing (and you will spend more $ for it).

What are we really looking for?
Polyester or nylon canvas that is heavy enough to take abuse. But not SO heavy that it doesn’t bend, or you can’t staple/sew through it.
Polyester and nylon have a high melting point, so you can iron-on bumper numbers.
You can “seal” the edges by using pinking shears (the toothed-edge or “zigzag” scissors)

  • All the fancy water-repellent, UV coatings (like in Sunbrella and Cordura) - not needed here, and it’s an added expense.
  • Acrylic… you are taking chances with it melting when you iron on numbers
  • Cotton - can tolerate some abuse, but will tend to rip at the staples (because we are ALL stapling this to the bumper backing right? Of course we are). Cotton or cotton/polyester canvas is a good choice if you have nothing else.

Great, so what the heck do I want?
My advice: Nylon or Polyester canvas (also called “Pack cloth” or “sailcloth”), 7 oz/yard.
7 oz/yard is a good baseline. It is tough, durable, but still easy to work with. You can go heavier if you like, but it will be stiffer and harder to work with.
(Fabric weights are intuitive - 1 oz/yard is parachute fabric, 11 oz/yard is super heavy, stiff canvas - much heavier than denim).

example: Seattle fabrics - nylon pack cloth 7 oz/yd
Full disclosure: I made a storage sling for my Soling out of this exact fabric. It can be sewn using a regular sewing machine, punched grommets through it, and the sling is still in great shape after 4 years on my boat, outside.

Where can I get this or something like it?
Online. Your local fabric store is probably not going to have what you need.
(If you are desperate and need something NOW - head to a local fabric store and look for the heaviest polyester, poly-cotton, or nylon canvas-woven fabric you can find. Probably in the upholstery section. DO NOT USE FELT. “Rip-stop” fabric tends to be very lightweight, but if you can find it heavy-weight it could work).

Seattle fabrics has been a great source for me (for sailing) and decent prices (not affiliated with them, just a good source I’ve used). You can even get a fabric sample set from them. Sample set I have
Sample set of all weights/types nylon fabric

Also amazon.com (naturally), fabric.com, diyardage.com , google…

FYI - you’re going to see “Denier” like it’s important or something. Its really not. “Denier” is just a measure of opacity. If the fabric is white, you can “see through” 50 denier, probably can’t see through 400 denier.

Our Team laser cut our own iron-on bumper numbers. (Have heard you can use a cricut as well)

Iron-on material we used : HTVront White Heat Transfer Vinyl (it is polyurethane, I checked)

To laser cut:
Material: Whatever you do, make sure whatever you use is NOT actual “vinyl”. Vinyl can be PVC (poly vinyl chloride) and anything with “chloride” on it is not laser safe (releases chlorine gas - bad for the laser, not good for you).

Image: reverse the image. You will be cutting from the back.

Power & Speed: On our Boss 100 Watt CO2 laser, we use 13% power, 75 mm/s travel speed. This will cut through the white polyurethane, but NOT cut through the clear plastic backing. It does discolor the back slightly, but that’s the side you will put against the fabric (so it won’t show).

"Weed" the image: remove all the white polyurethane around your numbers.

The official “how to iron on” instructions are below (from the vendor).
Iron on your numbers BEFORE you make your bumpers. I have not tested Ironing on with pool noodles underneath. Iron at your own risk!
These are for ironing onto a cotton t-shirt, so I ironed the bejeesus out of ours just to be sure, right onto our 7 oz/yd Seattle Fabrics nylon pack cloth.
I probably went overboard… but so far, these numbers are not coming off.

  • If using a household iron, please use the “cotton/linen” setting (usually the highest temperature setting). Make sure that the steam setting is off.
  • Preheat the application area of the substrate for 10-15 seconds.
  • Place the weed image (liner facing up) on the preheated material.
  • (I use a pressing cloth (muslin, old clean t-shirt, pillowcase) between the iron and the plastic carrier. I don’t really know this plastic, neither do you, and I am NOT going to clean plastic gunk out of my nice iron if it melts). Press the iron, hold it firmly for 15 to 30 seconds, then pick it up and move it - repeat until you’ve ironed the whole image. Do not slide the iron.
  • While the fabric is still warm, peel off the plastic carrier. If the vinyl starts to pull, put the plastic back and apply more heat.
  • Use a pressing cloth between the iron and the vinyl to press again for 10 seconds, then turn the item over and press from the back for 15 seconds.

Pics of a test to see how this worked.


Awesome info! Any advice for how to cut/fold the fabric to avoid having it bunch up in the inside corners?

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In sewing, you would “Miter” the corner.
Sewing mitered corners
Which isn’t exactly like a bumper, but gives you the basic idea.

The closest example I can find to a bumper is upholstery: Upholstery corners

Hope that helps!


I’ve done this a couple different ways. I’m a professional upholsterer, and even though I like to make them look pretty, we’re working with pool noodles and canvas. Both these examples have seen a season of play so they’re not as crisp as they used to be.

If youre making a rounded corners (noodles pulled around the corner instead of butted), you can pull through center tight and work the extra fabric away from the corner, then two inside folds toward the corner with the extra. I will staple on top and trim excess fabric inside the fold.

For square/butted corners (and to avoid sewing), it’s a similar process. I pull the excess fabric away from the corner nice and snug, staple on top of the frame, trim the excess from inside the fold and pull it neatly inside the edge.

I know this is hard to explain in text. Maybe this is the year I make a video as I upholster ours. I suggest taking some extra time to play with the fabric/folds and work it until you’re happy.

Beautiful write up @SurfGear !


Thank you @rocknthehawk Beautiful material work on your bumpers.

Do you ever use upholstery nails (such as the video I posted) when you make your bumpers?
Or do you work your way down the plywood backing, stapling as you go?
Do you typically staple on the raw selvage?
Ever fold it over for extra strength, or is that not worth it?
From the way the material is fraying on the blue bumper, I’m guessing a poly-cotton canvas material. Do you find that material tears at the staples (eventually)?


I like to tell new upholsterers - don’t be afraid of pulling staples out! I will staple in the middle, then pull super hard to each corner and put a staple in to hold it taught. Then work from my middle toward the corner. I pull out the corner staple and leave about 2" open from the corner. Then start to work my fabric at the corner into a fold.

I don’t use upholstery tacks very often- instead I pin tack with a staple (holding my staple gun off the surface so it doesn’t sink all the way in).

I typically don’t bother with the selvage or folding over for strength. I just pull it smooth, put a row of staples and trim off the excess. After years of doing then I started making sure I stapled in a relatively straight line to keep it neat. I usually cover the raw inside edge with matching colored gaffers tape or gorilla tape.

The frayed material is Cordura from AndyMark. This was torn from a piece of raw aluminum, not from cutting or stapling. I’ve never had issues with tearing, but I also use a pneumatic stapler and 3/8 staples.


Thank you both for this thread! It will be very helpful to all the rebuilding teams, new teams, etc.

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I LOVE learning of all the sewers that are also mentors!

I am a professional a well. I have sewn just about everything professionally. :rofl::rofl: From bridal gowns to bounce houses. Currently (for the last 25 years) I sew boat canvas, covers for the military, and marine upholstery.

The bumpers can be an interesting challenge. They can be very simple or extremely complicated depending on your desires and skill level. Bumpers can even be incorporated into the design of a mechanism (eg. intake). And if your not thinking about how your bumpers can help or hinder your design… you might be asking for trouble.

Fabric for bumpers need to be durable. Have a fabric you think will work? Place a wheel in a drill and spin it on a scrap piece of fabric for 10 min. Did it survive the test without much damage? I would consider that durable.

Get your fabric and Test it

Numbers can be iron on, painted, embroidered, or anything else that will last. Try it on scrap, then try the drill test. Did it work? Then it’s durable.
if you iron on, make sure the edges are pressed good

Get some fabric and practice

Our team usually has reversible bumpers with mitered corners. *We use “Weathermax” (brand name) This year we will be using a different fabric on the front to assist with the intake. (A vinyl that grips a little better, the weathermax is more ‘slick’)

We cut iron on numbers with a cricut. (You can also order them from RoboPromo)

My biggest advice is to think about the bumpers early and incorporate them into your design. You don’t want to build the robot only to find out you can’t attach the bumpers properly because your mechanism mounts are in the way. (Speaking from experience) And then practice making them, and test them.

**Sunbrella can handle iron on. We make bags from scrap at my work and iron on our company logo with a heat press and nothing melts. But it’s a little hard to sew without an industrial machine.

*We use Weathermax because I can get it free from work. It’s REALLY nice fabric and is light enough to be sewn with a heavy duty home machine (size 16 needle) if you don’t have an industrial machine. But it probably is overkill for bumpers.


Oh! A pneumatic stapler is an absolute must!


Tell us more about the reversible bumpers please!

I have seen them, love them, would love to learn more.


For an Epilog mini 18 (30 watt) the numbers we run are 50% speed and 12% power if anyone has an Epilog machine.

After all my years of doing this, I still think that reversible bumpers with a bungee cord are the best thing we ever developed for ease of use and speed.

On 696 we used Siser Easyweed for the numbers and cut them on a vinyl cutter. We found out iron to not get hot enough and it took too much time and effort. So, we bought a heat press from USCutter. Very worth it. Great tool.

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+1, great stuff and affordable too

Basically reversible bumpers let you change from red to blue without removing the bumper. It allows for quick changes and since you only have one set of bumpers, ensures you don’t have to run back to the pits to get the other set if you need to change.

The problems that can occur is that if the velcro doesn’t hold you may end up with more of the “other color” showing than is allowed by the rules. Or if it’s hanging during a climb it can invalidate a climb if it’s below the threshold. (Eg. Touching the ground)

You can correct these problems by using strong velcro across the entire length of the board. Don’t skimp and only put pieces. You can see in my photo above the black across the top of the bumpers where the wood is. That is all velcro. Stapled to the boards all the way down.

The red and blue fabric are placed together and sewn in the middle to create a “flap” that can be flipped up or down depending on what color you want. It can be time consuming to make, but my team loves the ease of use.

I’ll upload a few pics of a small front piece that never got put on (because the students had the wrong size) Hopefully they can clear it up somewhat.

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Oh and I just found this worksheet I did for my measurements. It might be helpful too. It’s a side cut view.

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Hook and loop can wear out and tear, 3/16 or 1/4 shock cord has been our go to for years.


Love it!
Does the shock cord run the entire length of the bumper?
Looks like it isn’t just a 4" piece at each corner.

Looks like you pre-sew the basic pattern with mitered corners where the red & blue fabric meet (where the bumper “turns over”) … do you then “try it on”, trim the corners for fit, THEN staple to the plywood?

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It is a big loop that at rest fits just inside the bumpers. It does lead to a bit of creativity to keep the cord off the wheels.

We put the fabric on the bumpers and then mark the miters, cut them, and hem the seams. Then when it is all done we press the numbers on and fish the cord through a loop seen in at the edge of the flap.


Wow, you use way more staples than we do. Thanks for the tips!


Alternatively, an electric staple gun. It doesn’t need an air compressor so it is easier to use and electric staple gun at events.

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