Modified Signal Logging file size gets very large

I have a singnal logging file generrated from a model that is about 2800 KB. I have a script that trims off the first 1 second of data to strip out iniitialization anomolies I do not care about. I also modified the data downsampling from 10 msec to 40 msec samples. When the script is complete the mat file is anywhere from 25,000, to 30,000 KB. Thsi makes the file much less shareable/portable. It would be nice to understand why the file sized increased so much and if there are any tricks?

Thanks,

Will