Over many years, like many of us, I've purchased other people's stamp albums and stamp storage binders to get the stamps I want. Most of these have been standard paper stamp albums where aging consists of gradually yellowing paper, presumably acidic paper, that yellows and degrades over the years as it gradually falls apart. We all know this, and none of us would reuse such pages. Yet many of us assume that both modern paper album pages and modern plastic pages must be safe or why would anyone sell them today if they weren't? Well, because they make money, that's why.
And I'm fairly sure that even the latest and the greatest paper album pages from the leading album manufacturers will only last just so long. I have some 50 year old paper stamp albums that are still in good shape, but of the 100-year old and older albums, none are in particularly good shape and some are browned and disintegrating badly. So that's your "modern paper lifespan" right there.
We don't know for sure what will happen to plastic album pages over the next 50 or 100 years, but I'm betting that they disintegrate, too. When a paper album page ages, it turns yellow and brownish which can in turn acidify the stamps mounted on it so that they turn brownish, as well. What will plastic pages do? More than likely the petroleum products used in their manufacture will gradually liquefy, making them feel more oily than when new. You can feel this oiliness on cheaply-made plastic pages after only a few years. That oil is more than likely going to ruin many stamps it comes into contact with, staining them and perhaps changing their color.
This may apply only to certain types of plastic but not other types -- or so they claim. I'm not quite convinced though that poly-this or poly-that is better than the other options, and since I know some plastic pages are very bad for stamps and covers -- and I've seen this with my own eyes -- I prefer to play it safe and avoid most plastic pages. I also do not like the weight of most plastic-page albums. They are just very heavy and I find that unpleasant.
With stamps mounted on paper pages in such albums, we are often advised to "air them out" periodically, something we do naturally when we look at our stamps and turn the pages. Presumably this lets the pages and stamps take a breath of fresh air, so to speak, although I'm not sure what actual benefit that has. With albums we haven't looked at in a long time, it might be a good idea to browse through them once in awhile. Old albums stored away for years without ever being looked at often contain disintegrated pages from aging which ruins stamps. Would they have fared better if they had been looked at? I haven't the slightest idea, but some claim so. Will "airing out" plastic-page albums make any difference to the life of stamps in them? I can't see how since the danger there is more than likely the oils in the pages themselves.
I decided not to use plastic page albums, but I do use plastic stamp mounts which might seem contradictory. But I've never seen a failed stamp mount other than the now ancient Crystal Mounts which fared very poorly over 50 years ago. Old stocks of Crystal Mounts can still be found on
ebay, amazingly, presumably sold to unsuspecting collectors. Some other brands of older stamp mounts I've seen have shrunk badly, ruining the stamps they hold. Some required the stamps to be literally sealed inside them which makes for a very difficult removal of stamps years later, often damaging the stamp. Stamp hinges with their "hinge remnant" problem never had that problem. And I've seen quite a few yellowed glassine envelopes and stocks books with glassine strips that have yellowed and aged badly, so glassine is not as safe as we once thought, either. I'm guessing everything used for collecting stamps probably degrades over time.
Bu I use Vario (clear non-oily plastic) pages for some volumes of First Day Covers I have. That I don't value FDC's particularly highly will be my excuse for that, but I've also never seen a degraded Vario plastic page -- though I have seen degraded plastic pages from other brands of "page protectors" and stamp storage pages. The lack of clear information about plastic stamp pages is one factor that makes me wary of them.
Over the years, I have seen a lot of oily, yellowed plastic stamp holders of various kinds. This convinced me that plastic album pages were to be questioned and maybe avoided. That I use stamp mounts is because the alternative is hinges which clearly do some small damage to stamps no matter what you do and mounts don't do that -- unless they degrade over time, and I've never seen modern mounts do that over many decades of use. So far, anyway.
So, all in all, I trust paper album pages when "aired out" -- but probably not over a hundred years. Long enough, I suppose. And I trust modern stamp mounts. Both have held up well enough and long enough. So far. On the other hand, I do not trust plastic stamp album pages because I suspect their disintegration will eventually do really serious damage to stamps.
Let's check back in 50 years -- and again in 100 years -- to see if I'm right.