I use these bags with my Medela pump and they fit perfectly. I was originally using Medela bags but decided to switch to these after doing a lot of research. Here's why:1- My number 1 gripe with the Medela bags is that THEY ARE NOT ACCURATE!! After pumping into their bags and then making bottles later I noticed that I always had less than what I thought I'd pumped. I did a little test and dumped 1 oz of water into a Medela bag and guess what? It read 2oz! The bags are off by exactly 1 oz which can mean the difference between a fat and happy baby and a hungry, grumpy baby. This discrepancy is strange since the markings on Medela bottles are accurate. It was when I discovered this inaccuracy that I really started doing research into other bags. WINNER: Honeysuckle2- These bags are biodegradable which I think is pretty darn cool. I'm not a tree hugger or anything but even I can see how pumping creates a ton of plastic waste with the bags. Medela bags are not biodegradable. While this wasn't initially something I cared a whole lot about it makes me feel good to know my bags wont be sitting in a landfill forever. WINNER: Honeysuckle.3- Obviously both bags fit directly onto Medela pumps however Honeysuckle hasn't released an adapter yet (I read on their website they will be releasing a universal adapter sometime in the near future) so you have to buy a box of Medela pump bags to get the adapter. I had 2 boxes of Medela bags and just accounted for the oz discrepancy to use them before switching to these bags. WINNER: Medela4- Medela bags are made of a thicker plastic which makes it easer to stand the bag up. I'm assuming the softer feeling plastic of the Honeysuckle bags are due to the biodegradability. Even though the plastic of the Honeysuckle bags feels softer it doesn't feel cheap or anything. I've never had a problem with leaking and I use a breastmilk organizer which compresses the bags so they'll freeze flat (B000K4YSVI I'm always very carful when standing the bag up because I do think that if you had less than say 2 oz in there it might tip over. I simply seal it before leaving it unattended and have never had a spill. I personally prefer the softer plastic as it is easier to get the bag open and manipulate than the stiff Medela bags. Since I think this is a matter of preference I'll call this one a TIE.5- These bags have a double seal while the Medela bags have a single seal which is a little hard to close. I've never had a leak with the Medela bags because I noticed early on that you have to press really hard to seal them and they're secure if you do it right. These bags are much easier to seal but just as secure. WINNER: Honeysuckle6- I've never had a leak with either bag but I would never freeze more than 1-2 oz in a Medela bag (marked as 2-3) . As I mentioned, I use a freezer organizer which compresses the bags and with 1-2 oz the milk in the Medela bags are already all the way to the seal and have expanded the bag. I think if you were to fill those bags to capacity they would burst but that's a hypothesis I wasn't willing to test with my hard won milk. As another reviewer noted, these bags are much longer than the Medela bags which gives the milk more than enough space to expand. I pump about 4 oz per bag, press out the excess air, and freeze with not problem. The milk never even reaches the seal and the bag doesn't feel like it's expanded width wise too much either. This saves me freezer space since I can freeze double the amount than I feel comfortable freezing in a Medela bag. WINNER: Honeysuckle7- As far as price goes, these are comparable if not a little cheaper than Medela bags. I've never purchased the Medela bags at a brick and mortar store but they're going for $16.69 on Amazon right now for a pack of 50. Honeysuckle bags are going for $15.25 right now for a pack of 50 (which comes in 2 packs of 25). That's 31 cents per Honeysuckle bag vs 34 cents per Medela bag. As numbers only this would go to Medela because their bags include the pump attachment but because of the poor capacity and wrong markings, you would end up using more bags than Honeysuckle. WINNER: HoneysuckleIt's been about 2 weeks since I've started using these bags and I won't be using any other brand. Hope this helps!UPDATE: 7/13/13I'm toward the bottom of my second 25 pack and the last two bags I pulled out (not the last two in the batch) had small holes in them. I was pumping and noticed milk dripping so I poured the milk into a bottle, filled the bag with water, sealed it and gave it a squeeze. Sure enough water came shooting out through a pin prick hole toward the bottom. I figured it was just a bad bag so I resumed my pumping session with a fresh bag and the same thing happened. I still have a couple in that pack but I don't want to use them for fear of losing my hard won pumped milk. I'll be contacting Honeysuckle about this but it's probably just a bad batch. The first 25 pack I used I had absolutely 0 problems with. Just something to look out for. There's no batch number on the bag to reference.