# The foam rubber in packing boxes -- how do they cut it so cleanly? **URL:** \ **Category:** Factual Questions\ **Created:** [November 18, 2002, 7:50pm UTC](https://boards.straightdope.com/t/the-foam-rubber-in-packing-boxes-how-do-they-cut-it-so-cleanly/137367 "2002-11-18T19:50:54Z")\ **Posts on this page:** 12\ **Page:** 1
**Author:** ![F.U.Shakespeare](https://avatars.discourse-cdn.com/v4/letter/f/aca169/32.png) [@F.U.Shakespeare](https://boards.straightdope.com/u/F.U.Shakespeare)\ **Post date:** [November 18, 2002, 7:50pm UTC](https://boards.straightdope.com/t/the-foam-rubber-in-packing-boxes-how-do-they-cut-it-so-cleanly/137367/1 "2002-11-18T19:50:54Z")
Does anyone know what tool they use? I’ve tried with shears and knives, and it always looks like h\*ll. ---
**Author:** ![keeper0](https://avatars.discourse-cdn.com/v4/letter/k/b19c9b/32.png) [@keeper0](https://boards.straightdope.com/u/keeper0)\ **Post date:** [November 18, 2002, 8:02pm UTC](https://boards.straightdope.com/t/the-foam-rubber-in-packing-boxes-how-do-they-cut-it-so-cleanly/137367/2 "2002-11-18T20:02:40Z")
Power tools specially designed for the job. Two pieces of metal clamp the rubber just to either side of the cut, and a really sharp bit slides between them to cut it. It can do this hundreds of times a minute. ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [November 18, 2002, 8:20pm UTC](https://boards.straightdope.com/t/the-foam-rubber-in-packing-boxes-how-do-they-cut-it-so-cleanly/137367/3 "2002-11-18T20:20:38Z")
A sharp butcher’s knife will do a clean job if you drag it along the surface, rather than sawing with it. It helps if you can keep the foam being cut under a bit of tension. ---
**Author:** ![3waygeek](https://avatars.discourse-cdn.com/v4/letter/3/e95f7d/32.png) [@3waygeek](https://boards.straightdope.com/u/3waygeek)\ **Post date:** [November 18, 2002, 8:22pm UTC](https://boards.straightdope.com/t/the-foam-rubber-in-packing-boxes-how-do-they-cut-it-so-cleanly/137367/4 "2002-11-18T20:22:58Z")
An electric carving knife works well for softer foam, such as is used in upholstery. ---
**Author:** ![RickJay](https://avatars.discourse-cdn.com/v4/letter/r/bb73d2/32.png) [@RickJay](https://boards.straightdope.com/u/RickJay)\ **Post date:** [November 18, 2002, 8:24pm UTC](https://boards.straightdope.com/t/the-foam-rubber-in-packing-boxes-how-do-they-cut-it-so-cleanly/137367/5 "2002-11-18T20:24:10Z")
I’ve audited a foam rubber packing company. Keeper is correct; they use large jigsaws, mostly, or very sharp knives. Depends on the specific peice and cut, but it’s all power tools. ---
**Author:** ![ElvisL1ves](https://avatars.discourse-cdn.com/v4/letter/e/5daacb/32.png) [@ElvisL1ves](https://boards.straightdope.com/u/ElvisL1ves)\ **Post date:** [November 18, 2002, 8:32pm UTC](https://boards.straightdope.com/t/the-foam-rubber-in-packing-boxes-how-do-they-cut-it-so-cleanly/137367/6 "2002-11-18T20:32:33Z")
Water jet machines are also well-suited for soft materials, and aren’t all that expensive. They also don’t have to be resharpened. ---
**Author:** ![Cartooniverse](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cartooniverse/32/3084_2.png) [@Cartooniverse](https://boards.straightdope.com/u/Cartooniverse)\ **Post date:** [November 19, 2002, 3:12am UTC](https://boards.straightdope.com/t/the-foam-rubber-in-packing-boxes-how-do-they-cut-it-so-cleanly/137367/7 "2002-11-19T03:12:25Z")
An added thought here. When I read the O.P., I thought that **F.U.** was referring to the custom-molded foam inserts that surround many items. In THAT case, rapidly expanding foam is jetted in against the plastic sheeting surrounding the item. It swells to fit the box, and protects the item. I used **FoamBoy** just tonight. It’s a cheap electric knife. I’ve had it for about 17 years, and as long as you spritz a bit of WD-40 onto the blades now and again, it will slice through high-density closed cel urethane foam rubber quite nicely. No, I won’t tell you what I was cutting !!! 😉 Cartooniverse ---
**Author:** ![Fear\_Itself](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/fear_itself/32/19637_2.png) [@Fear\_Itself](https://boards.straightdope.com/u/Fear_Itself)\ **Post date:** [November 19, 2002, 6:55am UTC](https://boards.straightdope.com/t/the-foam-rubber-in-packing-boxes-how-do-they-cut-it-so-cleanly/137367/8 "2002-11-19T06:55:35Z")
> [@](#): > > \*Originally posted by ElvisL1ves \* > \*\*Water jet machines are also well-suited for soft materials, and aren’t all that expensive. They also don’t have to be resharpened. \*\* Water + foam rubber = soggy mess? ---
**Author:** ![astro](https://avatars.discourse-cdn.com/v4/letter/a/9dc877/32.png) [@astro](https://boards.straightdope.com/u/astro)\ **Post date:** [November 19, 2002, 2:01pm UTC](https://boards.straightdope.com/t/the-foam-rubber-in-packing-boxes-how-do-they-cut-it-so-cleanly/137367/9 "2002-11-19T14:01:50Z")
I just got rid of three giant foam cutting jigsaws in perfect shape for scrap. They cost hundreds of thousands to put in place about 15 years ago. The equipment broker had no use for them because the motors and thin, hihg speed blades were too lightweight to use for anything else. I think they are using water jets now for foam cutting. ---
**Author:** ![drachillix](https://avatars.discourse-cdn.com/v4/letter/d/48db29/32.png) [@drachillix](https://boards.straightdope.com/u/drachillix)\ **Post date:** [November 19, 2002, 3:19pm UTC](https://boards.straightdope.com/t/the-foam-rubber-in-packing-boxes-how-do-they-cut-it-so-cleanly/137367/10 "2002-11-19T15:19:45Z")
> [@](#): > > \*Originally posted by Fear Itself \* > \*\*Water + foam rubber = soggy mess? \*\* Very thin stream of water at like 40,000psi, not a lot of water, just evil pressure. It also wont snag or scortch the material being cut like laser or mechanical cutting can. ---
**Author:** ![astro](https://avatars.discourse-cdn.com/v4/letter/a/9dc877/32.png) [@astro](https://boards.straightdope.com/u/astro)\ **Post date:** [November 19, 2002, 4:22pm UTC](https://boards.straightdope.com/t/the-foam-rubber-in-packing-boxes-how-do-they-cut-it-so-cleanly/137367/11 "2002-11-19T16:22:37Z")
[Here’s one of the foam cutting machines I had to trash last week](http://mywebpages.comcast.net/cpeek001/bandsaw.jpg) Notice the thin blade and small motor. ---
**Author:** ![Drew\_Blade](https://avatars.discourse-cdn.com/v4/letter/d/958977/32.png) [@Drew\_Blade](https://boards.straightdope.com/u/Drew_Blade)\ **Post date:** [November 19, 2002, 6:28pm UTC](https://boards.straightdope.com/t/the-foam-rubber-in-packing-boxes-how-do-they-cut-it-so-cleanly/137367/12 "2002-11-19T18:28:33Z")
The methods described here seem like they would make “straight” cuts. But I’ve seen some of “egg crate” foam rubber where you can’t even see the crack when the two pieces are put together. Any ideas on how these cuts are made? However it is done, it is good precision work.