I purchased the extra fine markers and was completely frustrated that they dried out after about a week with very little use, even though they were stored upside down as recommended, so I put the lids back on them and gave a hard shake, which made the ink flood out of the end of the pen but the tips were still dry. IRK! While cleaning the lids and pens from the mess I'd created, I noticed that water ran straight through the lids. DUH, no wonder why the tips are drying out! I slightly dampened the pen tips with an old cloth, sealed the lids with packing tape so air could not penetrate and reach the pen, stored them upside down for a few hours, and VIOLA, they work beautifully now. There is probably a logical explanation why expo manufactures the lids for airflow, but the reason escapes me. For now, my pens work and that's all that matters to me. Hope this helps someone else.