aluminum or steel

You don't want one of those fancy ones with the built-in suspension - they're too expensive ..

Aluminum seat posts are generally in the range of 4 or 5 times thicker than steel - so PLENTY strong particularly if they are made of a good alloy like 7005 or 6061 at T6 hardness.

Some of them are getting downright affordable, comparatively. (NOTHING is really "affordable" in bike parts right now)

Did you perchance mean to type "7075" aluminum ?

No, I meant 7005 which is the predominant alloy in bicycle construction worldwide.

Building bicycles or bicycle components from 7075 is pretty fiddicult as MOST of them require welding. Although not IMPOSSIBLE to wels, welding 7075 is NOT something you want to weld for a stressed component like a frame - OR a seatpost!!!

OK , I'd never heard of 7005 before you posted that . I did know that

Mine aren't. The fittings are bolted to a heavy wall extruded tube.

I think they are flat pieces bent into a circle and welding along the entire length. At least I think I remember seeing a weld line on some of them.

I've been reading the thread, in fact all 3 of milne, but just haven't had time to write answers. The eweather is beautiful and I've actually spent time out outdoors. I hope microsoft won't be angry at me.

Many are. The good ones anyway. The forged part the seat fastens to has to be connected to the tubular post. Some are shrunk / staked - some are bonded - and some are welded.

Aluminum posts are extruded or machined from billet not formed and seam welded. Steel posts are generally electrically welded tubing

Its a great idea if the bike manufacturer/distributer knows about your discussion.