i have found out a way to make a heater barrier out of high temp cork found in the hobby isle at walmart stores and at home depot hardware section.

video of it working here
http://www.youtube.com/watch?v=TZ994gv_HaA
and it running at 285C here
http://www.youtube.com/watch?v=aHnd-BPtAmw

go to walmart in crafts section and look for corks, these corks are temp capable to 300c, and fire retardant, will not catch fire.

go to welding section and get a pack of welding rod filaments .6mm, if not. at walmart then home depot.

for less that 10.00 you now have enough cork and welding rod filiments to make 6 or more replacement extruders.

parts you will also need that can be used again and again. a1 100k or 200k thermistor, and a fiberglass coated ni chrome wire about 5-6inches in length or about 4-5ohms.

also you will need 1 m6 nut, and a 1/4 inch hole 1/2 inch washer

get 1/8 drill bit and take a tiny piece of tubing and place it thru the drill bit, and reference the welding rod tip, so that 1-2mm of it extends past the drill bit, then with the tubing thur the drill bit, drill into the welding rod, until at reference where the welding rod is drilled into,

most likely the welding rod will be clogged with metal pieces. to get rid of those pieces in the .6mm hole, put a piece of plastic filament into the 1/ inch hole you just cut, thread the m6 nut onto the welding rod, and hold that part with a pair of pliers, then using a lighter, heat the copper welding rod, until the plastic starts to melt, then push the plastic thru until it goes thru the hole, then pull back. wait for welding rod to cool, then drill out the plastic. the tiny hole should now be unclogged, or it will be full of plastic that can melt later on...

now, hand drill 1/8 inch drill bit all the way thru the center of the cork piece, try to be centered if possible. then on the fat end that goes towards the welding rod piece, drill .4 -.5 inch hole .1 -.15 inches deep, you want it to be deep enough to guide the 1/8 inch hole with the 1/8 inch hole in the welding rod, but you want to form a compressive seal, so don\'t make it more than .15inch or more deep!

on the upper end of the cork barrier, use a .24 inch bit to taper the entry into the 1/8 inch hole, then, after that is done,

take kapton tape and wrap tightly around the cork, from top to boom and back 2 times around at least. this is because the cork does not have a lot of strength to hold together otherwise. you can use electrical tape if you would like, because the outside of the cork does not get hot enough to melt electrical tape except near the bottom.

you may want to use this part to hold the top in place if used on a rapman like i did here http://www.thingiverse.com/thing:3742

take 1, or 2 1/4 inch hole 1/2 inch wide washers, place beneath the welding rod piece, as in picture, the bold the part into place, as you would a normal ptfe piece with a normal barrel. you just want to make sure that the part forms a seal, so the bottom needs to compress at least a1/10of an inch into the m6 nut, and the cork needs to touch the washers, because otherwise there will not be a good seal and plastic will seep out. also have a piece of plastic filament inside the welding rod holder piece, and the cord, so when it is tightened down the 1/8 inch holes lineup

this design allows a very short heating region, I have only tried it with abs, but i can run my extruder all the way up to 285C! - this is my 4th try at the cork extruder, the method i demonstrated here works ok, just because the extruder is copper, you will want to preheat your extruder before you go into a program and use it, also you must file down the end of your filament, otherwise the cork will tear from the inside.

downside is the smallest filament is .6mm, i have no idea how long the cork barrier will last. my previous one was not taped on the sides, and blew out when i tried pushing filament thru at a lower temp that what can push at. also this extruder require temp to be about 5 deg c higher to flow correctly.