On one of the other forums someone stated that metal reels were more likely to cause VS and warping; can anyone explain why a film should warp stored on a metal reel anymore than if it was stored on a plastic reel? I have a few amateur films from the 1920s and 30s and they are fine, no sign of warping.

They state its something to do with interaction with metal spools and the acetate stock can help kick VS off. Same for the Metal film cans.

Warping can be caused by slack or poor rewinding onto the spool. Film should always be tightly wound with no slack or sag.

I've got some 400 footers that must have been stored in cans for years, no problems yet. I do have one 16mm feature in metal cans, and I do occasionally take the lids off to give them an airing. I wonder if that is any metal, some reels are steel, other aluminium?

I think for us when it comes to 1200ft spools you simply cannot beat the genuine Elmo metal reels. we have many of these and when you spin them they are dead straight,no side wobble at all. Not a single film we have on these has ever had any problems, and when you get near the end of a reel during projection you never get that annoying scraping sound that you get with cheap plastic reels. You know the noise dont you, when your audience starts looking back to see what the noise is?
Having said that, The American reel company spools,(800 foot reels) are also superb. Perfectly moulded with no strain on the film.
All our 400 foot spools appear to be plastic and with a few exceptions we dont normally encounter any problems, i always throw away any home made ones which have appeared on a few second hand films over the years as these are always well dodgy and almost certainly puts a strain on film during projection.
If the reels dont wobble and the film flows out perfectly, the spool is good. Any side wobble or scrappy noises, get shot of it.

I strongly dislike ALL plastic reels and try to avoid using them. In particular as take - up spools. They can be a right pain in the butt sometimes.

I use the Elmo 1200' as a take up reel, but on my smaller reel machines, it's plastic 400' ... They seem to work better for me