UV deterioration - That's why you don't leave the foam exposed. Foam serves it's purpose very well when used correctly. When left to sunlight exposure it really needs to be covered with sealant, flashing, wood, etc. to prevent this from happening.

Paul B, I've used your technique with a gun or two. As I recollect, it worked at least once. My beef is that they are sooo simple, yet completely unrepairable ( no replacement parts available, parts often very poorly-designed),... but expensive! The cans can be very unreliable, as well. Probably 50% of the cans I use - except in high-usage times - either clog up or won't stop running.

I dont have the experience you guys have BUT-I go to a church that the men of the church,not me,sealed up with foam 7 years ago.They filled the gap between where the soffit and brick wall meet because,in certain places,this is how the bats were entering the attic.In the past 2 years the bats have started reentering the same places they use to enter.I dont know if this is because of deterioration or the bats pricked at it.The church is two stories high so i would need a lift to get up there but i dont feel that the bats would be able to prick into it unless the foam has deteriorated.The foam is pretty strong when it drys.Only problem is this is under the eves and out of direct sunlight.I dont know if it makes a difference but the is the yellow color hardware store foam and not the black.About three years ago i bought [advanced bat control dvd],because thats all i could find on the subject.That dvd pretty much turned me from foam.I do feel foam is a great asset in certain situations but not always just because its a time saver.Not trying to stir things up,just my opinion.

Rugged, interesting opinion and one that I'm not going to argue. ( Mainly because of where you live ) The foam that you are talking about is one that we have avoided for just such reasons. I'm not sure that our northern bats could eat through the black foam faster than our ever-changing elements ( thawing and freezing ) could make a much nicer hole for them.

Dave I have the same beef as you and melting the foam only works part of the time. It really seems like some engineer would make a repairable one. It's like metro said you have to follow instructions and cover it if it is exposed to uv rays. I think one of the most important things is keep your foam warm all the time. Cold and hot seems to stop up the gun. Foam used properly is a good tool. I have made some repairs or exclusions that have been in place for 15 years. More than ten years ago at a wildlife job the customer mentioned a water leak in his basement. I offered to put foam in it at no charge and no guarantee. It is still holding without leaking.
If you give your client options and offer an exclusion for 150 dollars using wire and foam or a repair for 1200 dollars and the client chooses the exclusion I don't think you have done a bad or unprofessional thing.
I used to use foam a lot on bats with sealant on top or paint but I mostly replaced it with backer rod or some other backing with sealant. If it is a big enough gap that I am going to have to trim with metal wood or vinyl foam is a good filler behind it because it blocks out all air currents and with your trim in place the gap disappears to the animals senses. Most chew ins or tear ins started with an air current caused by sloppy construction or maintenance.
Every job is individual do good work, use the appropriate product charge accordingly. Foam is like guns or pain killers it can be abused but sometimes it is the right tool.
Rugged that geat foam turns to powder pretty quickly and this sounds like it probably needs a piece of trim put over a sealant. I am not cabable of doing it but pictures or measurments would be a good thread of its own for advice on this issue.

I feel the foam could breakdown from heat alone and not have to have direct sunlight on it.Is the pur foam or black foam suppose to be able to hold up longer.I'm just asking because i have never heard.When i was younger our 100 degree days in the summer usally lasted 2-5 days max.Now 3 weeks is the norm.I dont feel the bats can chew away anything but maybe they pick at it,it breaks down and falls out,or another animal removes it.I'm working on a bat job right now where the bats are gaining access to the eaves by going behind the vinyl siding where it meets at a chimney.They laid stylofoam boards over board walls and then the vinyl siding.There is damage where these 3 materials meet.Something has torn a gap in the stylofoam so the bats enter here,run the length under the vinyl to where the sheets of stylofoam meet[the carpenters left a 2 inch gap here instead of flushing them]and then strait up into the eaves where they roost.I dont feel the bats caused the entry point-maybe mice or birds.The point i'm finally getting to is this-the first thing to hit my mind was how quick this job could be with foam,but since i dont trust the foam i went with silicone caulking.

Rugged it sounds like the actual entry in the envelope is not very wide and silicone ws probably the right choice. That point probably does a lot of expanding and contracting and foam doesn't do that well and you can't paint it there either. Paint on vinyl to vinyl or brick doesn't look good either. If I used foam there it would probably be to fill the void out of my sight. Either a pre fab trim or one you made yourself would probably be a good thing also.

I read that pur is paintable. Whereas, pure silicon is not.

Tht spot sounds like a non paintable area so I would not use pur. If not going to cover with some kind of trim I would use clear sealant.

Yea I used white silicone-the 50 yr deal.The fireplace had where it necked down kind of like little steps-this is where the problem occurred.

Now that you described those little steps I know exactly what you are talking about and your silicone will be alright. I might have put some type of mesh wire and filled and covered it with the silicone.
I did one of those for sparrows and I did underfillwith foam then white silicone over it. I think Iput a wad of 1/4 cloth in before the foam but not necessary for tht spot as you have closed off the air current and sparroww and bat wont tear out your silicone. Sounds like you have it covered.

"The cans can be very unreliable, as well. Probably 50% of the cans I use - except in high-usage times - either clog up or won't stop running."

Dave made a good point. I have ended up with unusable cans of foam as well. Even after using multiple types of cleaners on the contact point they would not flow. I WISH TODOL WOULD MAKE SMALLER SIZED CANS FOR LESS WEIGHT ON THE GUN AND LESS WASTE WHEN THE CANS STOP FLOWING. (Maybe they heard me) As far as the guns go I agree they need to be made with "serviceable" in mind.