View Full Version : friend needs help

December 25, 2009, 06:56 AM
Hi. And thanks for reading the post.

I got my hands on some kevlar fabric and was told that to be of any use in a vest it has to be "truly compressed" I also got some kevlar thread and was thinking about stitching about 40 layers together.
Does anyone know how much the kevlar fabric should be compressed

The hard-type of kevlar which is not layers of fabric but one solid piece is generally regarded as being capable of absorbing the trauma of rifle fire, whereas the fabric type of kevlar is more associated with small arms fire, i know we may not all agree on this but it is a general concensus. What i am thinking is that if the fabric type of kevlar is compressed before being inserted into the pouch of a jacket this should be a good idea, how much can it be compressed?

Thanks for listening. John.

December 25, 2009, 10:31 PM
I was under the impression that class III trauma plates (for rifle fire) were made of compressed and kiln-fired boron carbide or another very hard ceramic and that soft body armor was simply many layers of kevlar sewn together with heavy nylon on the outside. I've never heard of compressing the kevlar layers beyond quilting them together.

Uncle Buck
December 26, 2009, 09:51 AM
Not exactly sure what you are trying to do here. But if you are thinking about making your own bullet 'proof' vest, I would recommend against it. (Who you gonna get to wear it during the testing?:eek:)

If you really want to compress it, you would need a very large press, with lots of pressure. You would also need some kind of glue like material to ensure it held together with the repeated wearings. Like bluejeans, the material (thread) will loosen as it is worn. You would have to find a way to re shrink the item each time to wear it/wash it.

Also, please remember that all kevlar is not created equal.
I worked with some engineers who designed an anti-helicopter landing area using kevlar rope strung above certain areas in order to deny landing to the aircraft. This stuff was fantastic and we never had anyone attempt to land. In theory, it should have worked. But it was not the same kevlar used in the maritime industry.

Some walls are now covered with a kevlar type material to resist explosions.

Some Jeans are now sewn with kevlar thread. (Geez, the jokes about a re-enforced crotch just keep jumping into my head.)

December 26, 2009, 12:39 PM
If you are making a vest, you would want to leave the kevlar fabric flexible. What it will stop will depend on how many layers it has. Modern armor uses inserts of hard, ceramics like boron carbide, alumina etc. to fragment the bullets before they hit the kevlar. It might be a fun home project for something like "box-of-truth" testing, but if you need a real vest buy one from a source with quality control and testing data behind the design. You can buy alumina plates from sources like Coors Ceramics or McDanel (http://www.mcdanelceramics.com/products.html), boron carbide is the best as it is very light and very hard but I do not know a convenient source.