I really liked these.  I purchased a red one to go under baby's lobster Halloween costume (also purchased on Amazon) because of its breathable fabric since it tends to get rather hot in Texas.  The product description states that this is good for babies that have sensitive skin.  My 4 month old does not, but I would imagine this would be helpful because of its ability to wick away moisture.  My child often gets sweaty in his carseat, and I noticed with this bodysuit on, he did not feel as clammy from sweating in the seat.  I would suggest to get in the larger size, for example, my baby is an average sized 4 month old but I purchased in the 6-12 months.  Not because the size runs small by any means, but the sleeves are easily folded back and stay that way if they are just a bit too big and the suit still fits well...so if you buy in a larger size, it will last longer in the long run.