Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What's happening: High-tech filtration company Polypore International's (UNKNOWN:PPO.DL) stock shot up as much as 13% today, before settling in at about 12.8% as of this writing. So far this year, the stock is up almost 27% already. 

Why it's happening: Polypore announced this morning that it was being acquired by Asahi Kasei Corporation for $60.50 per share. As part of the transaction, 3M (NYSE:MMM) is acquiring Polypore's Separations Media assets for $1 billion. It looks like the end of a great run for investors who bought shares at this time last year, as Polypore's stock has more than doubled:

PPO data by YCharts.

The transactions, of course, will be subject to approvals from all three companies' shareholders, so it's not clear when the transaction would be final. While it's probably unlikely that shareholders would get much upside from waiting to sell, you should consider the tax implications. If you've held shares for less than one year and in a taxable account, it would probably be wise to hold your shares until the one-year anniversary date to reduce capital gains taxes.