I teach recorder to young students (ages 9-11), and I often play along. I used to play on a Hohner wooden recorder, which I liked. It had a better tone quality and I thought it would be a better model for them to match. But the students play on Yamaha 24-B recorders (I did not want the headache of maintaining 50 wooden recorders!). This year I decided to switch to the Yamaha because the intonation between the two instruments was becoming an issue. I've noticed with the plastic recorder that after playing for several minutes, a noticeable amount of saliva/condensation builds up in the window/labium area (see attached picture below). After a while, enough liquid accumulates here that the recorder fails to produce a note unless I (rather indelicately) suck in from the mouthpiece to dislodge it. Is this an inherent difference between plastic and wooden recorders? Is it something like the plastic being non-porous and the wood being absorbent? For anyone who plays recorder seriously, how do you avoid this happening in performance?
With any plastic recorder you will always get some condensation due to the air coming from your lungs being very humid. This usually should not render the recorder unusable in a few minutes, unless your instrument is really cold. But if your technique is a bit "wet" you can get a lot of salvia into the mouthpiece. So try to play the recorder as dry as possible. Also it is common practise to warm up the recorder to body temperature before playing, to reduce or even prevent such condensation.
If your mouthpiece becomes too wet to play simply close the window with your hand and blow strongly into the mouthpiece. This should send out most of the liquid.
There is of course a difference between a plastic recorder and a wooden one. Wood is able to absorb humidity. This means that on a wooden recorder you will not get wetness from condensation as easily, as the wood will take in some of that water. But this is not in fact an entirely desireable thing: Too much wetness will make the block swell up a bit. Usually this would be taken into consideration when a recorder is build, but if the block swells too much it reduces the width of the wind channel, making the recorder hoarse.
One of the big advantages of a plastic recorder is that this cannot happen. A plastic recorder does not swell, and thus will only get hoarse due to condensation.